                              In the

    United States Court of Appeals
                For the Seventh Circuit
                    ____________________
No. 16-3102
UNITED STATES OF AMERICA,
                                                  Plaintiff-Appellee,

                                 v.

JEFFREY PARKHURST,
                                              Defendant-Appellant.
                    ____________________

        Appeal from the United States District Court for the
                      Central District of Illinois.
        No. 2:15-cr-20051-CSB-EIL-1 — Colin S. Bruce, Judge.
                    ____________________

       ARGUED MAY 22, 2017 — DECIDED JULY 25, 2017
                    ____________________

   Before FLAUM, EASTERBROOK, and SYKES, Circuit Judges.
    FLAUM, Circuit Judge. Jeffrey Parkhurst was convicted at
trial of attempting to entice a minor to engage in sexual activ-
ity and was sentenced to one hundred thirty-two months’ im-
prisonment. On appeal, Parkhurst challenges his conviction
and sentence. We affirm both.
2                                                     No. 16-3102

                           I. Background
    From January to July 2015, Jeffrey Parkhurst posted a se-
ries of internet advertisements on Craigslist’s “casual encoun-
ters” section. On July 20, for example, Parkhurst posted the
following ad:
       Gentleman Lookin For Young Son – m4m1
       (springfield)
       Tryin to find a very young white boy in order to
       spend some quality time together….he would
       be a little fella . kinda thin built . not too tall .
       clean kept . little to no body hair . average to
       good looking . (easy on the eyes lol) a little white
       guy who is friendly and fun to be
       around…sense of humor helps…18 or slightly
       older (younger the better)…must like to have a
       good time(not just sensual speaking)…prefer
       you to be a virgin . as far as guys are concerned .
       as I am myself one…like to do many different
       things that are fun …. must enjoy being close .
       being touched . massaged . rubbed all over with
       warming oil in a dim lit room and made to feel
       very erotic and sexy….nothing ever forced on
       you…goal is only to make you feel so good you
       will not want it to end ….ever lol….we can try
       about anything you have ever wondered
       about…you only need to ask !... Me ?... just an
       older discrete white guy that’s your age at heart
       and built like a teenager who just needs a dis-
       crete little friend to spend good times with…a

    1 “Male   for male.”
No. 16-3102                                                           3

        reply only cost ya a little time and may be the
        best thing you have done in a long time….be
        safe…be cool…be happy !!! Not looking for
        older guys so don’t waste your time or mine .
        thank you !
(ellipses in original). 2
   One week later, Decatur Police Detective Todd Koester
discovered Parkhurst’s advertisement and responded using
an undercover persona of 15-year-old “Kacy Lillard.” Kacy
(Detective Koester) and Parkhurst then exchanged text and
email messages for the next eight and a half hours:
    •   Kacy initiated the interaction, stating, “just wanted to
        say hi. im probably to[o] young but i am 15 and liek to
        hang out.”3 Parkhurst responded, “You are only too
        young if you can’t keep a secret lol . Hi buddy :)”
    •   Parkhurst stated that he “[w]ould love to give [Kacy]
        an erotic sensual massage covering every inch of [his]
        body in a candle lit room with a warming massage oil
        and supplies to do whatever [he] want[ed] to try.”
    •   Parkhurst asked Kacy whether he was “cut or uncut ….
        referring to [Kacy’s] penis.” Upon learning that Kacy
        was “cut,” Parkhurst stated, “Really glad ur cut , so am
        I.”


    2  Parkhurst’s advertisement included a number of typographical,
grammatical, and spacing errors that we have quoted without using
“[sic].” For the remainder of this opinion, the spelling and grammar ap-
pear as originally written unless altered with brackets.
    3 Later, Kacy messaged that he was “16” years old. Detective Koester
testified that this variation was unintentional.
4                                                     No. 16-3102

    •   Parkhurst proposed that he and Kacy “experiment and
        explore together and only try what both of [them]
        want[ed] to try.”
    •   Parkhurst expressed that he “[m]ay like to try and suck
        [Kacy].”
    •   In response to Kacy’s question, “U think any of its
        gonna hurt?,” Parkhurst answered, “I’ve been study-
        ing up on the subject so I know what to do to prepare
        you so it won’t hurt ! And I would not hurt you for the
        world buddy….I will be extra careful buddy cause I
        want both of us to want to do this over and over and
        not just a one time deal lol.”
Eventually, Parkhurst and Kacy agreed to meet that night.
Parkhurst planned to pick Kacy up at his Decatur apartment
(where Detective Koester and other officers would be sta-
tioned) at 11:30 PM after Kacy’s mother left for work.
Parkhurst would take Kacy to a truck stop for dinner, to
Parkhurst’s Springfield home for the night, and back to Deca-
tur by 7:30 AM the next morning before his mother returned.
Kacy messaged that he would need to shower and pack a bag
for the night, and Parkhurst responded, “Cool make sure ya
clean ur self extra good all over lol and i'll know if ya do later.”
While traveling to Decatur, Parkhurst offered to purchase
Kacy some candy, and stated, “[J]ust gotta promise not to eat
them all on the way back here lol.” Kacy asked, “Lol I won’t.
Y not?,” and Parkhurst responded, “Not my kinda candy ! It’s
all yours buddy….I’m pretty much gonna spoil you anyway
so get used to it ok ?”
   At about 11:30 PM, Parkhurst arrived at the Decatur ad-
dress Detective Koester had provided, and the police
No. 16-3102                                                      5

promptly arrested and interviewed him. Detective Koester
asked how old Parkhurst had believed Kacy was, and
Parkhurst answered, “I assumed I was—well, at one point
you said you were sixteen. So I assumed I was talking to a
fifteen or sixteen year old.” Parkhurst added, however, that
he had believed Kacy may have been lying about his age
given the multiple reported ages. Parkhurst acknowledged
that he had implicitly referenced oral sex in his conversation
with Kacy, and when asked whether someone reviewing
Parkhurst’s exchanges with Kacy could reasonably conclude
that Parkhurst had intended to engage in sexual activity,
Parkhurst responded, “Probably.”
   In a one-count indictment, the government charged
Parkhurst with attempting to entice a minor to engage in sex-
ual activity, in violation of 18 U.S.C. § 2422(b). After a trial, a
jury found Parkhurst guilty, and the district court sentenced
him to one hundred thirty-two months’ imprisonment and fif-
teen years of supervised release. This appeal followed.
                           II. Discussion
    Parkhurst appeals both his conviction and his sentence.
He requests a new trial by challenging the admission of parts
of Detective Koester’s testimony and the government’s use of
certain emails during cross-examination and in closing argu-
ments. Parkhurst seeks resentencing based on the trial court’s
use of an obstruction enhancement. We review for an abuse
of discretion the district court’s evidentiary rulings, United
States v. Williams, 272 F.3d 845, 856 (7th Cir. 2001) (citation
omitted), and sentence-enhancement decisions, United States
v. Vasquez-Hernandez, 834 F.3d 852, 854 (7th Cir. 2016).
6                                                  No. 16-3102

    A. Detective Koester’s Testimony
    Detective Koester served at trial as a dual fact-expert wit-
ness, discussing both his interactions (as Kacy) with
Parkhurst and his experience involving internet crimes
against children. Parkhurst challenges as unreliable two par-
ticular portions of Detective Koester’s testimony: his under-
standing of Parkhurst’s (1) “candy” comments, and (2) July 20
Craigslist ad. Lastly, Parkhurst contends that Detective
Koester’s dual fact-expert witness role confused the jury. We
consider each argument in turn.
       1. “Candy” Conversation
    Parkhurst first challenges the admissibility of Detective
Koester’s testimony regarding a candy-related conversation
he had (as Kacy) with Parkhurst. During direct examination,
Detective Koester described his understanding of the conver-
sation:
       Q: Okay. And then the rest of that portion of the
          conversation talks about your preference of
          candy, hard or chewy, et cetera. And then at
          8:44 p.m., tell us about this portion of the
          conversation.
       A: He responds at 8:44 saying, “Cool, just gotta
          promise not to eat them all on the way back
          here, LOL.”
       Q: And then your reaction?
       A: At 8:50 I respond, “LOL, I won’t. Why not?”
       Q: And what does he say?
       A: “Not my kind of candy. It’s all yours, buddy.”
No. 16-3102                                                      7

       Q: And what do you interpret that portion of the
          conversation to mean?
       A: At that point, I’m thinking he doesn’t want
          this 15-year-old kid to eat a lot of candy be-
          cause it’s gonna interfere with the sexual ac-
          tivity that’s supposed to take place.
       Defense: Objection, speculation.
       Court: Overruled. He can – he’s testifying as to
         what he understood the conversation in
         which he is a part of [sic]. Overruled.
       A: So, I’m thinking that he doesn’t want this kid
          to eat all this candy and get full because of
          the sexual activity that’s gonna take place; he
          doesn’t want him to be sick.
(internal quotation marks added). Parkhurst asserts that this
was expert testimony under Federal Rule of Evidence 702,
and argues that the testimony lacked the necessary discussion
of “methodology, expertise, or scientific method.” The gov-
ernment, however, contends that this was lay-witness testi-
mony, subject to Rule 701’s less-strict standards.
     Under Rule 701, “[i]f a witness is not testifying as an ex-
pert, testimony in the form of an opinion is limited to one that
is: (a) rationally based on the witness’s perception; (b) helpful
to clearly understanding the witness’s testimony or to deter-
mining a fact in issue; and (c) not based on scientific, technical,
or other specialized knowledge within the scope of Rule 702.”
Fed. R. Evid. 701. We review decisions to admit lay-opinion
testimony pursuant to Rule 701 for abuse of discretion.
Yancick v. Hanna Steel Corp., 653 F.3d 532, 547 (7th Cir. 2011)
(citation omitted). Rule 702 expert testimony, on the other
8                                                  No. 16-3102

hand, is based on a witness’s knowledge, skill, experience,
training, or education, and must be based on sufficient facts
and reliable principles and methods. Fed. R. Evid. 702. The
standard of review is also different: We review de novo
whether the court applied the required Rule 702 framework,
and for an abuse of discretion the court’s decision to admit or
exclude the expert testimony. United States v. Pansier, 576 F.3d
726, 737–38 (7th Cir. 2009) (citation omitted).
    Taken together, the government’s examination, Detective
Koester’s answers, and the district court’s ruling made clear
that Detective Koester’s testimony about the “candy” conver-
sation was based on his perception of the conversation at the
time it occurred—classic Rule 701 lay-witness testimony. The
government, for example, inquired about Detective Koester’s
“reactions” to Parkhurst’s messages, and Detective Koester
explained his view of the conversation “at that point.” And
the district court cleared up any confusion regarding the basis
for Detective Koester’s answers when the court overruled
Parkhurst’s speculation objection, clarifying that the detective
was testifying about his understanding of the conversation at
the time he was participating in it. As such, this testimony
need only satisfy Rule 701’s requirements. The district court
held that it did, and we see no abuse of discretion in admitting
it.
       2. July 20 Craigslist Advertisement
    Detective Koester was qualified as an expert without ob-
jection and gave expert testimony on the ways in which child
predators use certain key words in Craigslist advertisements
No. 16-3102                                                                  9

to evade detection, 4 basing his awareness on years of experi-
ence in investigating online child abuse and on relevant train-
ing. 5 Detective Koester then testified about his particular un-
derstanding of Parkhurst’s July 20 Craigslist ad:
        Q: Now, I believe your testimony yesterday dis-
           cussed certain parts of advertisements that
           you look for that are indicative to you, based
           on your training and experience, of individ-
           uals who may be seeking a minor. What
           parts of [Parkhurst’s] ad struck you [when
           you first saw it on July 27]?
        A: Well, the first line, “very young white boy, a
           little fella.” The “18 or slightly older,” right
           in parentheses after that, “younger the bet-
           ter,” that struck me as something that some-
           body — okay, I’m complying with Craigslist
           rules by putting 18 or slightly older, but
           I’m —
        Defense: Objection, speculation.


    4 Detective Koester testified that he had learned how to identify sus-
pects who may be committing crimes against children online and about
these suspects’ methods and means of committing such crimes. He also
explained Craigslist to the jury, describing the website’s advertisements
service, its “flag” function (used to identify illegal practices), and its pop-
ularity among child-predators.
    5 The government proffered Detective Koester as an expert witness in
online child-abuse investigations, presenting his (1) level of education (a
Master of Science degree); (2) experience in conducting over twenty-five
online investigations involving crimes against children; (3) relevant train-
ing for online undercover investigations for which he had received certi-
fications; and (4) attendance at related regional and national conferences.
10                                                No. 16-3102

      Government: Your Honor, this witness has been
        qualified as an expert and can testify to his
        training and experience and why this ad
        struck him.
      Court: The objection’s overruled actually for the
        reasons [the government] states. He’s been
        qualified as an expert in online investiga-
        tions. He’s able to testify as to … his experi-
        ence and give his expert opinion.
      A: The — in parentheses right after the “18 or
         slightly older” where it says “the younger
         the better,” that’s a way for people to get
         around the Craigslist terms and conditions
         basically without saying younger. That’s just
         a hint to people reading it. “Prefer you to be
         a virgin.” Built — basically him describing
         himself as built like a teenager. Those are the
         main things that struck me.
      Q: Okay. Now, you had testified that the “18 or
         slightly older” but in parentheses “younger
         the better” was, in your opinion, a way to get
         around the Craigslist terms of use; is that
         right?
      A: Correct.
   Parkhurst argues that Detective Koester’s expert testi-
mony was inadmissible under Rule 702 because the court did
not determine whether Detective Koester’s investigative
methods “ha[d] been tested, … subjected to peer review and
publication, whether there [was] a known rate of error, [or]
No. 16-3102                                                    11

whether there [was a] general acceptance in the field in eval-
uating the reliability of the proffered testimony.” See Fed. R.
Evid. 702; Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S.
579 (1993). He also asserts that this testimony constituted an
opinion about Parkhurst’s subjective motivations in violation
of Rule 704(b), imputing to Parkhurst the nefarious intent of
targeting minors with his advertisement.
    At the outset, “[E]xpert testimony must be helpful to the
jury to be admissible.” United States v. Christian, 673 F.3d 702,
710 (7th Cir. 2010). Detective Koester first described
Craigslist’s “flagging” function that identifies and blocks im-
proper uses of Craigslist features by scrutinizing the words
users include in their advertisements. He then presented and
interpreted various “[k]ey words”—such as “young,” “fresh,”
and “barely used”—that, in his experience, individuals use to
target minors without running afoul of Craigslist’s regula-
tions. Finally, he highlighted which words in Parkhurst’s ad-
vertisement appeared, based on his expertise, to constitute
such key words. We see no appreciable difference between
this testimony and that of narcotics officers describing “code
words” for drugs that we have previously deemed helpful to
the jury. See United States v. York, 572 F.3d 415, 423 (7th Cir.
2009) (concluding that an FBI agent’s expert testimony about
the meaning of the words “six, “nine,” “five dollar,” and
“fifty-five” within a conversation was helpful); United States
v. Ceballos, 302 F.3d 679, 689–88 (7th Cir. 2002) (concluding that
DEA agents’ interpretations of “it,” them,” and “both” as re-
ferring to methamphetamine shipments was helpful). Detec-
tive Koester’s key-word testimony helped the jury apply to
the evidence alternative theories of which they ordinarily
may not have been aware. See Ceballos, 302 F.3d at 687–88; see
also United States v. Christian, 673 F.3d 702, 711 (7th Cir. 2012)
12                                                    No. 16-3102

(“What might seem like innocuous conduct to an untrained
jury, might, to the trained eye, be indicative of criminal activ-
ity.”).
    Parkhurst’s focus on scientific-reliability factors is mis-
placed. Detective Koester’s expert testimony was based on his
extensive training and experience in over twenty-five investi-
gations involving internet crimes against children. Training
and experience are proper foundations for expert testimony.
Fed. R. Evid. 702 advisory committee’s note to 2000 amend-
ment (citations omitted) (“the text of Rule 702 expressly con-
templates that an expert may be qualified on the basis of ex-
perience. In certain fields, experience is the predominant, if
not sole, basis for a great deal of reliable expert testimony”);
see also Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137, 156
(1999) (“[N]o one denies that an expert might draw a conclu-
sion from a set of observations based on extensive and spe-
cialized experience.”). We have repeatedly allowed such ex-
pert testimony without requiring “scientific methodologies”
or “peer review.” See United States v. Conn, 297 F.3d 548, 555–
56 (7th Cir. 2002) (citing cases); see also id. at 556 (“[T]he Daub-
ert factors … ought not be considered a definitive check list
suitable for the evaluation of all kinds of evidentiary submis-
sions involving specialized knowledge … . [W]e have noted
specifically that genuine expertise may be based on experi-
ence or training.”) (citations and internal quotation marks
omitted). Instead, district courts ruling on the admissibility of
expert testimony of investigating law-enforcement officers
may review factors such as the officer’s years of experience
and number of investigations. See id. (citations omitted). The
district court in this case did just that, and, in light of Detec-
tive Koester’s extensive experience investigating internet
No. 16-3102                                                                13

crimes against children, it was not an abuse of the court’s dis-
cretion to qualify Detective Koester as an expert witness or to
admit his expert testimony regarding Craigslist advertise-
ments. 6
    Parkhurst’s contention that Detective Koester’s testimony
violated Rule 704(b) meets the same fate. Normally, “[i]n a
criminal case, an expert witness must not state an opinion
about whether the defendant did or did not have a mental
state or condition that constitutes an element of the crime
charged or of a defense. Those matters are for the trier of fact
alone.” Fed. R. Evid. 704(b). We have explained, however,
that,
        when a law enforcement official states an opin-
        ion about the criminal nature of a defendant’s
        activities, such testimony should not be ex-
        cluded under Rule 704(b) as long as it is made

    6 Expert testimony regarding “code words” may inherently be untest-

able in a scientific manner given the ever-changing nature of these words
over time and across groups of individuals. While this may call for height-
ened scrutiny by trial courts (i.e. through specific, cautionary jury instruc-
tions) or vigorous cross-examination by opposing counsel regarding the
testimony’s believability or applicability, it does not render the testimony
inadmissible due to unreliability. In the related context of code words in
narcotics cases, we have noted: “Experts need not establish that certain
words have fixed meanings only in the narcotics world or in the particular
conspiracy before they can interpret those words. Experts can determine,
based on their expertise, that certain words have drug-related meanings
within the context of a single conversation.” York, 572 F.3d at 424 (empha-
sis added). The same principle applies here. Detective Koester testified,
based on his expertise in internet crimes against children, about certain
“key words” that refer to minors in the context of Craigslist advertise-
ments. Based on our precedent, the basis of this testimony was sufficiently
reliable.
14                                                            No. 16-3102

         clear, either by the court expressly or in the na-
         ture of the examination, that the opinion is based
         on the expert’s knowledge of common criminal
         practices, and not on some special knowledge of
         the defendant’s mental processes.
United States v. Lipscomb, 14 F.3d 1236, 1242 (7th Cir. 1994) (em-
phasis added); see also United States v. Winbush, 580 F.3d 503,
512 (7th Cir. 2009) (“Although an expert may not testify or
opine that the defendant actually possessed the requisite
mental state, he may testify in general terms about facts or
circumstances from which a jury might infer that the defend-
ant intended to [commit the charged crime].”). What matters
is the degree to which the expert refers to the specific defend-
ant’s intent; expert testimony is proper as long as it leaves for
the jury the ultimate conclusion that the defendant intended
to commit the charged crime. Id. (citation omitted). Here, the
government’s examination made it clear that Detective
Koester’s testimony regarding the July 20 Craigslist advertise-
ment was based on his background knowledge of criminal ac-
tivities on Craigslist and not on Parkhurst’s mindset. The gov-
ernment asked Detective Koester what about the advertise-
ment had stood out to him, “based on [his] training and expe-
rience.” 7 He then identified and interpreted various words in

     7
     Indeed, the government referred to Detective Koester’s testimony
from the previous day, in which the detective had explained his
knowledge of common online-predator practices:
         Q: Okay. Are there other indicators within the ad that you
             are trained to look for to determine whether or not
             that person is looking for an adult or looking for a mi-
             nor?
         A: Yes.
No. 16-3102                                                       15

Parkhurst’s advertisement that, based on his experience, re-
sembled “[k]ey words” that other individuals have used to
target minors without violating Craigslist’s regulations. De-
tective Koester never mentioned Parkhurst’s “intent” or
“mindset,” and he never directly testified that Parkhurst in-
tentionally sought to sexually entice minors—which is what
our precedent prohibits. See, e.g., United States v. Collins, 715
F.3d 1032, 1038 (7th Cir. 2013) (expert testimony admissible
where officer’s testimony was not based on “some special fa-
miliarity with the workings of [the defendant’s] mind”) (inter-
nal quotation marks omitted); United States v. Are, 590 F.3d
499, 513 (7th Cir. 2009) (“We affirmed the district court's deci-
sion to allow the expert testimony because the officers testi-
fied that their opinions were based on their knowledge of
‘common practices in the drug trade’ and not on ‘some special
familiarity with the workings of [the defendant's] mind.’”) (ci-
tations omitted); United States v. Blount, 502 F.3d 674, 679–80
(7th Cir. 2007) (approvingly noting that the testifying officer
“never referred to [the defendant’s] ‘intent’ or ‘intentions’”



       Q: What are some of the things that you look for?
       A: Key words such as “young, fresh, barely used,” just
           certain terms throughout the ad that — kind of their
           way to disguise their posting so it doesn’t get re-
           moved by Craigslist, yet to convey to their audience
           what they’re looking for.
       Q: And did you find an ad on July 27th, 2015, that was
           actually posted about a week earlier, on July 20th,
           2015, with the title Gentleman Looking For Young
           Son, dash, M4M, in parenthesis, Springfield?
       A: That is correct.
16                                                  No. 16-3102

and holding that the officer’s expert testimony “did not trans-
gress Rule 704(b)'s limitations”); Lipscomb, 14 F.3d at 1242 (no
Rule 704(b) violation where an expert testified “that a certain
pattern of conduct evinces a particular kind of criminal activ-
ity”). No reasonable juror could have believed that Detective
Koester’s testimony was based on some special knowledge of
Parkhurst’s intent. Considering the examination as a whole,
the testimony did not violate Rule 704(b).
       3. Dual Role
    As a final matter, Parkhurst claims that Detective Koester’s
dual role as a fact-expert witness confused the jury. However,
we routinely uphold the practice of presenting dual fact-ex-
pert witnesses, “particularly where experienced law enforce-
ment officers were involved in the particular investigation at
issue.” York, 572 F.3d at 425 (citation omitted); see also United
States v. Lightfoot, 224 F.3d 586, 589 (7th Cir. 2000) (“there is
nothing wrong with having a police officer testify both as a
fact witness and an expert witness”) (citation omitted). True,
there are “inherent dangers with this kind of dual testimony,”
such as jury confusion, id. (citations omitted), but this “poten-
tial for prejudice … can be addressed by means of appropriate
cautionary instructions and by examination of the witness
that is structured in such a way as to make clear when the
witness is testifying to facts and when he is offering his opin-
ion as an expert.” Id. (quoting United States v. Mansoori, 304
F.3d 635, 654 (7th Cir. 2002)). These precautions tell the jury
what it needs to know to determine how much weight to give
the testimony and the opposing counsel what he needs to
know to cross-examine the witness effectively. United States v.
Moreland, 703 F.3d 976, 983–84 (7th Cir. 2012).
No. 16-3102                                                       17

    Contrary to Parkhurst’s assertions, the district court and
government took appropriate precautions against the poten-
tial for jury confusion. The district court instructed the jury as
follows:
       You have heard witnesses, [including] … Detec-
       tive Todd Koester, who, in some instances, gave
       opinions and testimony about certain subjects,
       specifically, … online investigations involving
       minors. You do not have to accept these wit-
       nesses’ opinions or testimony. You should judge
       these witnesses’ opinions and testimony the
       same way you judge the testimony of any other
       witness. In deciding how much weight to give
       to these opinions and testimony, you should
       consider the witnesses’ qualification, how they
       reached their opinions or conclusions, and the
       factors I have described for determining the be-
       lievability of testimony.
While it is advisable that trial courts distinctly instruct jurors
to not give the witness’s lay testimony any extra weight
simply because the witness is an expert, we have previously
deemed acceptable instructions nearly identical to this one.
See Moreland, 703 F.3d at 984. Furthermore, as described in
more detail above, the government’s examination made clear
the basis for Detective Koester’s answers—that is, whether a
given answer was fact testimony regarding the investigation
in this case (i.e., Rule 701 testimony) or expert testimony de-
rived from his experience in similar investigations (i.e., Rule
702 testimony). This is all we require of the examining party.
See id. at 983–84; see also id. at 983 (“Telling the jury that a wit-
ness is both a lay witness and an expert witness and will be
18                                                            No. 16-3102

alternating between the two roles is potentially confusing—
and unnecessary.”). As such, Detective Koester’s dual testi-
mony was unproblematic.
     B. Parkhurst’s Emails
    Parkhurst next argues that the government inappropri-
ately questioned him about email communications with other
individuals who had responded to his casual-encounter ad-
vertisements. 8 He additionally argues that the government
committed prosecutorial misconduct by referring to stricken
evidence related to these communications during its closing
arguments.




     8Below are relevant portions of a few of the emails the government
referenced during cross-examination:
     •   Exhibit 19B: Parkhurst corresponded with a purported 14-year-
         old male, writing, “I would just like to give you a full body mas-
         sage and just see where it ends up , promise you will enjoy it for
         real :) only will do whatever you want to at the moment and
         would never force anything on you I promise you that !!!”
     •   Exhibit 19D: Parkhurst corresponded with a purported 15-year-
         old male named Hunter. When Parkhurst learned of the pur-
         ported minor’s age, he responded, “You would have to be able to
         keep this totally secret and not tell a single person, not even your
         best friend , nobody !!!!!”
     •   Exhibit 19G: Parkhurst corresponded with a purported 20-year-
         old male who represented that he was “160 5'10 6.5 cut straight”
         and had not “been with a guy in a while.” Parkhurst replied,
         “Even though I do like the pic you sent, I am really kinda looking
         for someone like myself that has not done anything yet with a guy
         … .”
No. 16-3102                                                19

      1. Evidentiary Rulings
    Parkhurst first argues that the district court incorrectly
ruled that Parkhurst had “opened the door” to cross-exami-
nation on his emails. During direct examination, however,
Parkhurst discussed his internet advertisement and associ-
ated communications, and asserted that he only wanted to in-
teract with of-age individuals, i.e., those eighteen years or
older:
      Q: Okay … when you posted your ad, what
         were you hoping to accomplish?
      A: I was hoping to meet someone of age and de-
          velop a relationship with them.
      …
      Q: When you were emailing back and forth with
         Detective Koester’s undercover fake person-
         ality[,] Kacy, what were you hoping to ac-
         complish? Be honest.
      A: If this person was actually of age, I was hop-
          ing to meet up with him [to start a sexual re-
          lationship].
      …
      Q: Okay. And even after you knew that the per-
         son maybe was under 18, you continued to
         talk?
      A: Correct.
      Q: Why?
      A: It was a — it was somebody to talk to. I mean,
          it was pleasant. It was — like I said, I’m
20                                               No. 16-3102

          lonely, you know. Somebody was carrying
          on a conversation.
      …
      Q: When you had this conversation, … what did
         you hope was going to happen?
      A: I was hoping this person was 18 or older, like
          my ad said.
      …
      Q: Did you ever intend to force or persuade
         someone under the age of 18 to have sex
         with you?
      A: Not at all.
      Q: Did you want to have sex with somebody un-
         der the age of 18?
      A: Not at all.
      Q: What, what was your ultimate goal from all
         these ad posts that you put up?
      A: To be with someone between 18 and 25.
The district court held that Parkhurst’s testimony had
“opened the door” for the government to question Parkhurst
about the emails—particularly those in which he had con-
versed with purported minors:
      As soon as the defendant began to stress the fact
      he was looking for [“]of age[”] — and he re-
      peated that multiple times in his answers — that
      certainly began heavily knocking on the door, if
      not opening it….So, based upon the cumulative
      nature of both his answers and stressing [“]of
No. 16-3102                                               21

      age[“] and your question where you pursued
      what he would do with conversations with peo-
      ple underage, the door has been opened. The
      government may use the [emails] that I’ve re-
      viewed … to cross-examine the defendant….I
      can tell you that when you asked your client —
      when you headed for that e-mail communica-
      tion section … you not only opened the door,
      you basically drove a truck through it….I find
      that [the emails] are not improperly prejudicial,
      and they are, in fact, probative so they can be
      admitted. But, of course, extrinsic evidence is
      not admissible, so you can cross-examine him
      about those.
The government then proceeded to cross-examine Parkhurst
with the emails, using them to discredit the notion that
Parkhurst had only wanted to interact with of-age individu-
als:
      Q: Okay. And so you told Detective Koester that
         you had never talked to anybody that you
         believed to be 15?
      A: Correct.
      …
      Q: That’s not true, though, is it, Mr. Parkhurst?
      A: Well, you really don’t know how old any-
         body is on Craigslist.
      Q: The question that Detective Koester asked
         you is, Did you ever talk to anyone that you
22                                              No. 16-3102

         believed was 15 years old on Craigslist, and
         you said, “No, never.”
     A: Correct.
     Q: Correct? But that is not true. You did talk to
        people … other than Kacy that you believed
        were 15 and other minor ages, correct?
     A: I wasn’t sure of their age.
     …
     Q: Based on reviewing Government’s Exhibit
        19D … [d]id you have a conversation with a
        person that portrayed themselves to be a 15-
        year-old?
     A: Someone that portrayed theirself [sic.] as 15,
        yes.
     Q: Okay. And your response when that person
        asked you if they had to be over 18 was “not
        if [you] can keep a secret”; is that right?
     Defense Attorney: Objection, extrinsic evidence.
     District Court: No, this is proper impeachment.
     A: Correct.
     Q: So, when I asked you earlier if you had a con-
        versation with someone who you believed to
        be 15, and you said you didn’t know what
        their age was, you certainly knew enough to
        tell them to keep a secret, correct?
     A: Correct.
     …
No. 16-3102                                                           23

        Q: And [Exhibit 19D] is an e-mail transaction
        with an individual who identifies himself as
        Hunter, correct?
        A: …. Correct.
        Q: And the exhibit that you just reviewed now,
        I believe, is 19B; is that correct?
        A: Correct.
        Q: That is a different individual, correct?
        A: Correct.
        Q: What did you believe his age to be?
        A: Well, he said he was 14.
(internal quotation marks added). The government did not
move to enter the emails into evidence, and so the district
court did not admit them. 9
    Parkhurst asserts that the district court erred by allowing
the government to impeach him about his email communica-
tions with other individuals purporting to be minors, arguing
that they were not in evidence. We review the district court’s
ruling for an abuse of discretion. United States v. Kohli, 847 F.3d
483, 492 (7th Cir. 2017) (citations omitted).
    “It is well-settled that when a criminal defendant elects to
testify in his own defense, he puts his credibility in issue and

    9 After the government’s cross-examination, the court concluded that
the government’s questioning was appropriate: “[A]ll of the exhibits used
by the government or the manner in which they impeach was appropriate;
they were directed toward the truthfulness of the defendant’s statements;
and … counsel for the government had a good-faith basis to ask those
questions.”
24                                                   No. 16-3102

exposes himself to cross-examination, including the possibil-
ity that his testimony will be impeached.” Id. (citation omit-
ted). As illustrated above, Parkhurst testified multiple times
that he was only interested in interacting with of-age individ-
uals. These repeated assertions put his credibility in issue and
thus opened the door for the government to question the
truthfulness of his testimony—particularly, by inquiring
about his conversations with purported minors. See id.
Parkhurst’s claim that the district court allowed the govern-
ment to use the emails as extrinsic evidence conflates cross-
examination of an issue with use of extrinsic evidence. See
United States v. Sanders, 614 F.3d 341, 344–45 (7th Cir. 2010)
(“[T]he rules of evidence make a distinction between cross-
examination as to an issue and the use of extrinsic evidence
regarding it.”). While “extrinsic evidence is not admissible to
prove specific instances of a witness’s conduct in order to at-
tack or support the witness’s character for truthfulness[,] …
the court may, on cross-examination, allow them to be inquired
into if they are probative of the character for truthfulness or
untruthfulness of … the witness.” Fed. R. Evid. 608(b). (em-
phasis added). The government did not seek to enter the
emails to impeach Parkhurst; instead, it cross-examined him
about his interactions with purported minors and accepted
his answers without contradiction. Cf. Kohli, 847 F.3d at 493
(identifying the same distinction regarding the related “col-
lateral evidence rule”); Simmons, Inc v. Pinkerton’s, Inc., 762
F.2d 591, 605 (7th Cir. 1985), abrogated on other grounds as
recognized by Glickenhaus & Co. v. Household Int’l, Inc., 787
F.3d 408, 425 n.12 (7th Cir. 2015) (describing the “collateral ev-
idence rule as “now incorporated into Rule 608(b)”). In sum,
the district court correctly found that Parkhurst had opened
No. 16-3102                                                  25

the door to his emails and that the government had appropri-
ately impeached him; it was within the court’s discretion to
admit Parkhurst’s testimony given that he had waded into the
emails with his eyes open.
       2. Prosecutorial Misconduct
   Parkhurst next argues that the government committed
prosecutorial misconduct during its closing argument by
mentioning a previously-stricken line of testimony regarding
another child, Hunter. The government had the following ex-
change with Parkhurst during cross-examination:
       Q: Now, the individual who identified himself
          as Hunter in Government’s Exhibit 19D, you
          actually continued and had a text message
          conversation with him; is that right?
       A: Correct.
       Q: Would it surprise you to know that Detective
          Koester found the individual last night?
       A: No.
       Q: And he was actually 15.
       A: Okay.
       Defense Attorney: Objection, move to strike, but
          too late now.
       District Court: Well, sustained. The jury will dis-
          regard that question and that answer.
Later, during closing arguments, the government reviewed
the evidence tailored to Parkhurst’s sexually-explicit interac-
tions with Kacy (Detective Koester). Parkhurst’s counsel re-
26                                                            No. 16-3102

sponded in part by referring to both Parkhurst’s testimony re-
garding his desire to exclusively interact with of-age individ-
uals and his email exchanges with purported adults. During
its rebuttal argument, the government highlighted the incon-
sistencies in Parkhurst’s testimony regarding the emails:
         Let’s compare what the defendant says to what
         the evidence shows. He says to Detective
         Koester, I never talked to anyone who I believed
         to be 15 years old. But you saw that when I
         cross-examined him and showed him the e-
         mails in Government Exhibit 19, that group, he
         was talking to a 15-year-old named Hunter. He was
         talking to a 14-year-old. He said he was hoping
         to meet somebody of age, he was not interested
         in anyone under 18, and only looking for people
         18 to 25. But you saw on cross-examination that
         an experienced 23-year-old, an experienced 20-
         year-old he rejected. Too much experience. But
         an experienced 16-year-old, that was fine.
(emphasis added). Parkhurst made no objection.
    Parkhurst argues that the government’s rebuttal argument
relied on the previously-stricken testimony regarding
Hunter’s real age. 10 “Improper prosecutorial comments dur-
ing closing arguments are reviewed under a prosecutorial



     10 This was problematic, Parkhurst claims, for a variety of reasons: the

“Hunter” evidence demonstrated that Parkhurst had a propensity to sex-
ually engage with minors; it was hearsay within hearsay—Hunter’s state-
ment to Detective Koester within Detective Koester’s statement to the gov-
ernment; and it violated the Confrontation Clause, as Parkhurst was not
given the opportunity to confront either Detective Koester or Hunter.
No. 16-3102                                                             27

misconduct framework.” United States v. Richards, 719 F.3d
746, 764 (7th Cir. 2013) (citation omitted). “This analysis re-
quires, first a determination that prosecutors acted improp-
erly, and second a conclusion that the improper conduct prej-
udiced the defendant.” Id. (citation omitted). The govern-
ment’s allusion to Hunter in rebuttal was not improper be-
cause it was not in reference to the stricken testimony, as
Parkhurst asserts. Rather, the statement was based on
Parkhurst’s testimony regarding his own email exchanges
with Hunter—which, as described above, the government ap-
propriately elicited after Parkhurst had opened the door to
impeachment through his email interactions. This testimony
about Hunter was separate and apart from the stricken testi-
mony about Hunter’s real age.
    In any event, Parkhurst cannot show that the govern-
ment’s alleged misconduct prejudiced him. “When gauging
prejudice, we consider the remarks in light of the entire record
to determine if the defendant was deprived of a fair trial.” Id.
at 766 (citation and internal quotation marks omitted). Fur-
ther, “[w]here the defendant fails to object to the remarks at
the time they were made, the plain error standard … requires
that the defendant establish not only that the remarks denied
him a fair trial, but also that the outcome of the proceedings
would have been different absent the remarks.” United States

Parkhurst’s parade of horribles ends before it begins. Each of these argu-
ments addresses the admissibility of the stricken “Hunter” evidence, but it
was just that: stricken evidence (that was never admitted). The government
asked an arguably inappropriate question, Parkhurst answered, his coun-
sel objected, and the district court sustained—possibly for the reasons
Parkhurst now lists. None of this is relevant to whether the government’s
closing arguments—during which no party enters evidence into the rec-
ord—were improper.
28                                                  No. 16-3102

v. Sandoval, 347 F.3d 627, 631 (7th Cir. 2003) (citation and in-
ternal quotation marks omitted). Parkhurst cannot meet this
standard, given the plethora of unchallenged evidence re-
garding Parkhurst’s interactions with Kacy (Detective
Koester). In his email and text messages with Kacy, for exam-
ple, Parkhurst, upon learning that Kacy was purportedly fif-
teen years old, responded that Kacy was “only too young if
[he could not] keep a secret.” Later, in his post-arrest state-
ment to Detective Koester, Parkhurst explained that he had
thought Kacy may have been lying about his age but had still
assumed he was talking to a fifteen- or sixteen-year-old. De-
spite that assumption, Parkhurst had then made sexually-ex-
plicit offers, asking Kacy whether he was “cut or uncut”; ex-
pressing that he “may like to try and suck [Kacy]” and pro-
posing that they “experiment and explore together”; explain-
ing that Parkhurst knew “what to do to prepare [Kacy] so it
[would not] hurt”; making clear that Parkhurst “want[ed]
both of them to do this over and over”; and, finally, arranging
and attempting to pick up Kacy at his Decatur apartment to
take him back to Parkhurst’s Springfield home. This evidence
alone was sufficient to support Parkhurst’s conviction. Con-
sidering the record as a whole, Parkhurst cannot show that
the government’s alleged misconduct prejudiced him.
     C. Parkhurst’s Sentence
   Lastly, Parkhurst argues that the sentencing court erred by
enhancing his mandatory-minimum ten-year sentence to el-
ven years based on the court’s finding that he had obstructed
the proceeding by asserting his innocence during trial.
Parkhurst, however, has waived this challenge, as he only cur-
sorily identifies it in his opening brief, failing to present any
legal authority or make any supporting arguments. See United
No. 16-3102                                                   29

States v. Beavers, 756 F.3d 1044, 1059 (7th Cir. 2014) (“Perfunc-
tory, undeveloped arguments without discussion or citation
to pertinent legal authority are waived.” (quoting Mahaffey v.
Ramos, 588 F.3d 1142, 1146 (7th Cir. 2009))).
                         III. Conclusion
   For the foregoing reasons, we AFFIRM the judgment of
the district court.
30                                                           No. 16-3102

    EASTERBROOK, Circuit Judge, concurring. Although I join
the majority’s opinion, I write separately to observe that the
instruction discussed at pages 16–18 is not the best that dis-
trict courts can do. Parkhurst neither objected to the lan-
guage quoted at page 17 nor proposed something better, but
trial judges should be able to give juries more help than this
instruction did.
    Detective Koester testified in two capacities: an expert on
some issues, he was a lay witness on others. In his expert ca-
pacity he helped the jury understand code language used on
the Internet to find or attract targets for sexual exploitation;
in his other capacity he told the jury about his investigation
of and exchanges with Parkhurst.
     [W]hen a witness … testifies in a dual capacity, the district court
     must take precautions to minimize prejudice to the defendant.
     The witness’s dual role might confuse the jury, or a jury might be
     smitten by an expert’s aura of special reliability and therefore
     give his factual testimony undue weight. Experts famously pos-
     sess an aura of special reliability surrounding their testimony.
     And it is possible that the glow from this halo may extend to an
     expert witness’s fact testimony as well, swaying the jury by vir-
     tue of his perceived expertise rather than the logical force of his
     testimony. Or, the jury may unduly credit the opinion testimony
     of an investigating officer based on a perception that the expert
     was privy to facts about the defendant not presented at trial. Al-
     ternatively, the mixture of fact and expert testimony could, un-
     der some circumstances, come close to an expert commenting on
     the ultimate issue in a criminal matter.
     In light of such dangers, district courts must take some precau-
     tions to ensure the jury understands its function in evaluating
     this evidence. The jury needs to know when an agent is testify-
     ing as an expert and when he is testifying as a fact witness. The
     dual testimony situation places an especially heavy burden on
     the district court to ensure that the jury understood its function
     in evaluating the evidence, particularly where the conduct at
No. 16-3102                                                             31

   question may appear innocent. To take the necessary precau-
   tions, the court can give an appropriate cautionary instruction
   and require examination of the witness in such a way as to make
   clear when the witness is testifying to fact and when he is offer-
   ing his opinion as an expert. Other precautions include the gov-
   ernment establishing the proper foundation for the witness’s ex-
   pert opinions and the district court allowing rigorous cross-
   examination.

United States v. Christian, 673 F.3d 702, 712–13 (7th Cir. 2012)
(citations and internal quotation marks and other punctua-
tion omitted). By that standard, the instruction given to
Parkhurst’s jury falls short. It does not tell the jury “when an
agent is testifying as an expert and when he is testifying as a
fact witness.” Nor does it tell the jury not to let the witness’s
expertise on some matters influence its evaluation of his tes-
timony about the facts of the case.
     The district court adapted its language from a precursor
to Instruction 3.13 of the Pattern Criminal Jury Instructions of
the Seventh Circuit (2012 ed.). Instruction 3.13 and its prede-
cessor in the 1999 edition were designed for use with wit-
nesses testifying solely as experts. That’s why it does not
mention the issues that affect dual-capacity witnesses. The
Committee on Federal Criminal Jury Instructions could do
litigants and district judges a favor by drafting a new in-
struction for dual-capacity witnesses. Until that happens, lit-
igants and judges should address these issues on their own.
    The first step is pinning down exactly which elements of
a given witness’s testimony reflect expertise and which re-
flect knowledge gained as a participant in or investigator of
a given case. The parties’ appellate briefs disagree about
which parts of Detective Koester’s testimony reflect which of
his capacities. They did not try to work out these differences
32                                                   No. 16-3102

in the district court through draft instructions or submis-
sions to the district judge, so I appreciate the trial judge’s re-
luctance to address them on his own. Still, the jury needs
help, and district judges ought to prompt the parties on the
subject.
    Language that will warn juries not to let respect for ex-
pertise carry over to fact-specific testimony can be drafted
for use in all similar cases. Here is a simple possibility: “This
witness’s special knowledge about [expert subject] does not
make his testimony about [lay subject] more reliable than
that of any other witness.” Perhaps the Committee will come
up with an improvement. Particular language is less im-
portant than conveying the idea.
    Analysis of a legal problem, such as the discussion in
Christian, can affect the conduct of criminal trials only when
lawyers and district judges address the problems and put
concrete advice in jury instructions. That was not done in
Parkhurst’s case because the lawyers did not flag the prob-
lem and propose an appropriate treatment. The fact that to-
day’s opinion, like United States v. Moreland, 703 F.3d 976,
983–84 (7th Cir. 2012), accepts language along the lines of
Instruction 3.13 as sufficient does not mean that this instruc-
tion ought to be given. District judges should do better than
the legal floor.
    Moreland is problematic in its own right. Decided nine
months after Christian, which it does not cite, Moreland told
district judges the opposite of Christian in some respects. It
asserted that distinguishing between lay and expert compo-
nents of a single witness’s testimony is unnecessary and con-
fusing to the jury. 703 F.3d at 983–84. We may need to resolve
this intra-circuit conflict in some future case. The panel to-
No. 16-3102                                                 33

day sides with Christian in identifying dual-capacity testi-
mony as a potential problem on which jurors need infor-
mation, and with Moreland in approving a jury instruction
that fails to distinguish the two kinds of testimony. This ten-
sion cannot endure indefinitely. The parties to today’s appeal
have not addressed the tension, let alone asked for its resolu-
tion, which can wait for a case in which the subject has been
briefed.
