                FOR PUBLICATION

  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT


UNITED STATES OF AMERICA,                No. 14-30056
                Plaintiff-Appellee,
                                            D.C. No.
                v.                       3:12-cr-00373-
                                              HZ-1
SAMUEL NAVARRETTE-AGUILAR,
AKA Guayabo,
             Defendant-Appellant.          OPINION


     Appeal from the United States District Court
              for the District of Oregon
     Marco A. Hernandez, District Judge, Presiding

               Argued and Submitted
           March 3, 2015—Portland, Oregon

               Filed December 28, 2015

     Before: Raymond C. Fisher, Richard A. Paez,
         and Sandra S. Ikuta, Circuit Judges.

                Opinion by Judge Paez
2         UNITED STATES V. NAVARRETTE-AGUILAR

                           SUMMARY*


                          Criminal Law

    The panel affirmed in part, reversed in part, and vacated
in part a criminal judgment in a case in which a jury
(1) found the defendant guilty of conspiracy to distribute
heroin, distribution of heroin, and possession of heroin with
intent to distribute; and (2) made a special finding that the
quantity of heroin was at least one kilogram, triggering a
mandatory minimum twenty-year sentence under 21 U.S.C.
§ 841(b)(1)(A)(i).

    The panel concluded, as did the district court, that the
testimonial and physical evidence cannot support a finding of
one kilogram. The panel held that the district court erred,
however, in determining that the pattern of transactions
permitted the jury to conclude that members of the conspiracy
would have eventually distributed one kilogram of heroin.
The panel wrote that it would be speculative to infer that the
defendants agreed to any future transactions such that they
would reach the one kilogram mark. The panel held that the
error was not harmless, and therefore reversed the jury’s
quantity finding, vacated the sentence on all counts, and
remanded for re-sentencing.

   Affirming the convictions, the panel held that the district
court did not abuse its discretion when it permitted the
government to ask the defendant’s sister, a defense witness,
about the defendant’s prior convictions, where the witness

  *
    This summary constitutes no part of the opinion of the court. It has
been prepared by court staff for the convenience of the reader.
         UNITED STATES V. NAVARRETTE-AGUILAR                    3

opened the door to impeachment. The panel concluded that
even if the district court did abuse its discretion, the error was
harmless.


                          COUNSEL

Per C. Olson (argued), Hoevet Boise Olson Howes, Portland,
Oregon, for Defendant-Appellant.

Kelly A. Zusman (argued), Appellate Chief, Assistant United
States Attorney and S. Amanda Marshall, United States
Attorney for the District of Oregon, Portland, Oregon, for
Plaintiff-Appellee.


                          OPINION

PAEZ, Circuit Judge:

    Samuel Navarrette-Aguilar (“Navarrette”) appeals his
conviction and sentence. A jury found him guilty of
conspiracy to distribute heroin, distribution of heroin,
possession of heroin with intent to distribute, and made a
special finding that the quantity of heroin was at least one
kilogram. Navarrette argues that substantial evidence did not
support the jury’s quantity finding. The evidence of historical
transactions adduced did not amount to one kilogram.
Navarrette maintains that when the district court denied his
motions for judgment of acquittal, it erred in determining that
the pattern of transactions permitted the jury to conclude that
members of the conspiracy would have eventually distributed
one kilogram of heroin. Navarrette further argues that the
district court abused its discretion when it permitted the
4       UNITED STATES V. NAVARRETTE-AGUILAR

government to ask a defense witness on cross-examination
about his prior convictions for drug trafficking and escape.
Although we affirm Navarrette’s convictions on the
conspiracy and distribution counts, we reverse the district
court’s ruling on the jury’s quantity finding, vacate his
sentence, and remand for re-sentencing.

                             I.

    Navarrette was charged with Conspiracy to Traffic Heroin
in a quantity of one kilogram or more; Distribution of Heroin
Resulting in Death; and Possession with Intent to Distribute
Heroin. 21 U.S.C. §§ 841, 846. He was also charged with
the penalty provision for distributing a kilogram or more of
heroin, 21 U.S.C. § 841(b)(1)(A)(i), which provides for a
mandatory minimum twenty-year sentence for a defendant
who, like Navarrette, has a prior felony drug conviction. The
government also charged him with the penalty provision for
distributing a schedule I controlled substance resulting in
death or serious injury, 21 U.S.C. § 841(b)(1)(C). The
government charged two co-defendants along with
Navarrette: Saul Guzman-Arias, who proceeded to trial with
Navarrette, and Antonio Equihua-Ramirez, who pled guilty
and became a witness for the prosecution.

    A jury trial commenced on June 4, 2013. Because this
appeal turns on whether there was substantial evidence to
support the jury’s finding that Navarrette and his co-
defendants conspired to distribute at least one kilogram of
heroin, we discuss the evidence produced at trial in detail.
         UNITED STATES V. NAVARRETTE-AGUILAR                       5

    The government investigated and prosecuted Navarrette
as a “Len Bias”1 case—that is, they sought to prove a supply
chain directly linking the top of the chain, Navarrette, to the
heroin overdose death of a woman named Erin Freeman.
Distribution of a schedule I or II narcotic resulting in a death
or serious injury carries a twenty-year mandatory minimum
sentence, and a mandatory life sentence for those with a prior
felony drug conviction. 21 U.S.C. § 841(b)(1)(C). Seeking
this heavy penalty, the government sought to prove the
connections among the members of the supply chain. As the
evidence at trial showed, the investigation proceeded by using
information from lower-level dealers to pursue higher-level
distributors.

    The government presented the jury with a narrative of the
investigation process through the testimony of several
officers, including Portland Police Officer Tim Manzella.
Officer Manzella testified that, with the assistance of
Freeman’s boyfriend, he set up a controlled purchase of
heroin from her immediate supplier, Bruce McDaniel. While
watching McDaniel’s house, Officer Manzella saw Josef
Burns arrive; after he left, Manzella conducted a traffic stop


 1
        Many of the provisions of 21 U.S.C. § 841, including
        the twenty-year minimum prison term for causing a
        heroin overdose death, are often referred to as the Len
        Bias laws after a popular college basketball star. Len
        Bias played basketball for the University of Maryland
        until a drug overdose caused his untimely death in
        1986. Congress enacted the provisions of 21 U.S.C.
        § 841 under the theory that but for their purchase of
        drugs the overdose victims would not have died.

Katherine Daniels & Carol M. Bast, Difficulties in Investigating and
Prosecuting Heroin Overdose Cases, 41 Crim. L. Bull. 513, 517 (2005).
6         UNITED STATES V. NAVARRETTE-AGUILAR

of Burns. During their encounter, Burns admitted that he was
McDaniel’s heroin supplier.         Officer Manzella then
engineered another controlled purchase of heroin using
Burns, which led local law enforcement officers to the next
supplier up the chain, Antonio Equihua-Ramirez. Equihua-
Ramirez was arrested at the buy location, and officers found
sixty-two grams of heroin and between $7,600 and $7,800 in
cash in his vehicle. Equihua-Ramirez agreed to cooperate
with the police and consented to a search of his home, where
police found approximately thirteen grams2 of heroin. Officer
Manzella testified that Equihua-Ramirez had told him that the
cash in his car was the profits from his sale of 150 grams of
heroin, which he planned to turn over to his supplier, who had
“fronted” him the drugs. Additionally, upon seizing Equihua-
Ramirez’s phone, Officer Manzella found a text message,
sent to a number later determined to be Navarrette’s, in which
Equihua-Ramirez attempted to place an order for eight more
pieces of heroin (200 grams) once he finished selling what he
had.

    Using Equihua-Ramirez, officers set up another
controlled buy, this time from Equihua-Ramirez’s supplier,
whom he knew as “Califas,” for the 200 grams that Equihua-
Ramirez had already attempted to order. Officers arrested
Saul Guzman-Arias, who appeared at the appointed time.
Equihua-Ramirez identified him as the go-between who
delivered the drugs that Equihua-Ramirez ordered from
“Califas.” Officers searched Guzman-Arias’s car and


    2
    Throughout their testimony, witnesses used different measurements –
ounces, pieces, and grams – to describe the quantities of their transactions.
An ounce is approximately twenty-eight grams; a “piece” is approximately
twenty-five grams. We have converted all measurements to grams using
this scale.
        UNITED STATES V. NAVARRETTE-AGUILAR                  7

recovered 199.03 grams of heroin (the eight piece order) from
a hidden compartment, capable of holding up to forty pounds
of contraband, in his car. The police officers obtained cell
site information relating to the phone Equihua-Ramirez used
to place orders for heroin and used GPS to find the location
of the phone he called, belonging to “Califas.” Police
arrested “Califas,” revealed to be Navarrette, at his home.
They did not find any drugs, but they did recover $1,860 in
cash, and also discovered a large hidden compartment in his
vehicle that could have held up to thirty pounds of
contraband. Thus, the total amount of heroin recovered and
presented as physical evidence at trial was approximately 274
grams.

    In addition to the physical evidence, the government
presented several defendants’ phone records, as well as a few
wiretapped calls from a federal investigation that had also
ensnared Guzman-Arias, but none of these yielded evidence
of the specific quantity of heroin transacted. Instead, the
phone records presented, which included the records of
Equihua-Ramirez, Navarrette, and Guzman-Arias, showed the
number and frequency of calls and text messages among
several members of the conspiracy. Local law enforcement
officers also testified that they used a call placed from
Equihua-Ramirez to Navarrette to triangulate the location of
Navarrette, in order to arrest him, as evidence of Navarrette’s
identity as “Califas.” As none of these other pieces of
evidence would permit the jury to find that the conspiracy
involved at least a kilogram of heroin, the government’s main
evidence of quantity came from the testimony of Equihua-
Ramirez and Burns.

   Burns testified that, during the time period alleged
(approximately two and a half months, from mid-March to
8       UNITED STATES V. NAVARRETTE-AGUILAR

early June), he only purchased heroin from Equihua-Ramirez,
and Equihua-Ramirez testified that he only purchased heroin
from Navarrette. Equihua-Ramirez further testified that
Burns was his biggest customer, and his “[a]bout five” other
customers only bought about a gram of heroin at a time,
without specifying in greater detail how much heroin they
purchased. Therefore, the government had to prove an
agreement to distribute a kilogram of heroin from either
a) Equihua-Ramirez’s testimony as to how frequently he
purchased heroin from Navarrette; b) Equihua-Ramirez’s
testimony as to how frequently he sold heroin to Burns; or
c) Burns’s testimony as to how frequently he purchased
heroin from Equihua-Ramirez.

A. Testimony of Josef Burns

    Josef Burns could not state with certainty how many
times and in what quantities he had purchased heroin from
Equihua-Ramirez. For example, Burns initially stated that he
had purchased heroin “more than a dozen times,” but later
said that he “[did]n’t know [how many times].” When
pressed on cross-examination, he agreed that a more realistic
range was twelve to sixteen transactions, and stated “I mean,
whatever. I mean, I’m not sure. I can’t exactly say.” On
cross-examination, Burns also waffled on how long he had
been buying from Equihua-Ramirez:

       Q. Yeah. Is it possible your relationship
       started sometime in late April?

       A. In April?

       Q. Correct. So it would have been about a
       month and a half?
        UNITED STATES V. NAVARRETTE-AGUILAR                 9

       A. March, April, something like that. April,
       May, June, yeah, something around there.

       Q. You don’t really have a definite memory of
       that?

       A. I don’t have a definite—I don’t have a
       definite time on that.

    Describing his purchasing practices, Burns stated that he
began by buying “one piece [twenty-five grams] and then two
or three.” He testified that he could not estimate the total
amount of heroin that he purchased, but that it took him “a
month or two” to “wor[k] up to two or three pieces.” We
note again that the entire time period of the conspiracy
alleged was approximately two and a half months. When
questioned about the frequency with which he purchased
heroin, Burns stated that it could be one or two times a week,
but also “maybe a few more times . . . maybe three or four
max.” He went on to explain that the frequency with which
he purchased and the amount he purchased “would all just
depend” on the level of demand, which was “different all the
time.” The variation in the amount Burns purchased is borne
out by other record evidence. Notably, on May 26, Burns
received a text message from Equihua-Ramirez asking him
why he was not purchasing more heroin. When presented
with this evidence, Burns responded

       Yeah. I think I just—I just hadn’t called them
       in a little bit or whatever. I was not very—I
       didn’t really want to sell heroin. I did it
       because I didn’t know what else to do, really.
       I couldn’t do what I used to do, any of the
10       UNITED STATES V. NAVARRETTE-AGUILAR

        jobs I used to do. But I didn’t want to do it.
        I just did it because—I don’t know.

    Burns testified several times that he had difficulty
remembering details of the time period in question. For
example, when questioned more specifically about his
practice of selling heroin, Burns answered, “I’m trying to
think. I’m not prepared for all this. I can’t really remember.”
And, later, Burns stated in response to further questioning:
“I’m not really on it. . . . I just had a lot going on in the last
year since this happened so I haven’t been dealing with any
of this.”

    In sum, Burns’s testimony was vague; he could not
provide an estimate as to how much heroin he sold or
purchased, and could not clearly remember or describe his
practices during the time in question.

B. Testimony of Antonio Equihua-Ramirez

     Like Burns, Equihua-Ramirez gave equivocal testimony
regarding the frequency with which he bought and sold
heroin. Officer Manzella’s testimony revealed that, before
trial, Equihua-Ramirez contradicted himself in his statements
to the police. For example, he initially told Officer Manzella
that he had been dealing for a period of six months, but later
stated that he had only been dealing since mid-March. It
“seemed to [Officer Manzella] that he was pretty confused
about the exact start and end date.” Equihua-Ramirez also
gave different statements to police at different times
regarding the amount that he sold to Burns.

   At trial, Equihua-Ramirez testified that he began selling
heroin in March of 2012, upon taking over the business of a
        UNITED STATES V. NAVARRETTE-AGUILAR                11

friend of his while that friend returned to Mexico. It was to
be a temporary arrangement. Equihua-Ramirez only bought
drugs from “Califas,” the name by which he knew Navarrette.
Navarrette “fronted” him the drugs, meaning that Equihua-
Ramirez only paid for the drugs after he sold them to others,
and did not order more until he had sold all of the drugs that
he had previously bought. It also meant that he did not buy
more than he thought he could sell.

    Equihua-Ramirez testified that he began by ordering an
ounce (twenty-eight grams) at a time, which would take him
about three days to sell. Equihua-Ramirez further testified
that he purchased drugs “thirteen or fourteen” times.
Equihua-Ramirez later testified that he purchased heroin from
his supplier “between ten and thirteen [times],” but that he
“[did]n’t remember well.” He maintained that it could not
have been fewer than ten times.

    Equihua-Ramirez testified that, while he did not always
purchase a single ounce (28 grams), the most that he ever
purchased at a single time was four ounces (112 grams),
which he did shortly before he was arrested. However, his
last order had been for 200 grams; this would have been his
largest order.

    Equihua-Ramirez testified that Josef Burns was his
biggest customer, and that the last sale that he made to Burns
was for fifty grams. He further stated that Burns usually
purchased “sometimes one, sometimes two” pieces at a time
(twenty-five to fifty grams), and once purchased three pieces
(seventy-five grams). At one point, Equihua-Ramirez
testified that there was a period in April during which the
heroin was bad, and his customers stopped buying from him;
he stated that, as a result, he sold heroin only once in the
12       UNITED STATES V. NAVARRETTE-AGUILAR

month of April. He further testified that the poor quality of
the heroin angered him, and that he wanted to quit as a result.
He later testified, however, that the period in which Burns
refused to buy from him was approximately fifteen days, that
Burns then bought an ounce (twenty-eight grams) from him
in order to test the quality, and that he did not recall when that
purchase had taken place.

    Like Burns, Equihua-Ramirez did not concretely or
consistently testify as to the number of transactions or their
amount, and no clearer pattern of sales emerges from his
testimony than from Burns’s.

C. The District Court’s Ruling and Order

    The jury found Navarrette and Guzman-Arias guilty of
the Conspiracy, Distribution of Heroin, and Possession
charges, but did not find true that the distribution of heroin
resulted in the death of another. The jury, however, found
true that Navarrette conspired to distribute a kilogram or
more of heroin. After the verdict, Guzman-Arias renewed his
motion for judgment of acquittal under Rule 29 of the Federal
Rules of Criminal Procedure, arguing that the evidence was
insufficient as a matter of law to establish that the conspiracy
involved a quantity of at least one kilogram of heroin;
Navarrette joined in the motion, which the court denied in a
written order.

    The court first summarized the evidence discussed above.
Noting that the testimony of both Burns and Equihua-
Ramirez was vague and failed to specify the total quantity of
heroin that either purchased, and applying the substantial
evidence standard from United States v. Nevils, 598 F.3d
1158 (9th Cir. 2010) (en banc), the court employed two
          UNITED STATES V. NAVARRETTE-AGUILAR                       13

different approaches to determine the amount of heroin that
the jury could have found without speculation.

    First, the court analyzed the amount of heroin the jury
could have inferred from Equihua-Ramirez’s testimony as to
the number of purchases he made from Navarrette through
Guzman-Arias. Construing the evidence in the light most
favorable to the prosecution, id. at 1161, the court concluded
that the jury could have found that Equihua-Ramirez
purchased heroin fourteen times, and that the last purchase
was for 100 grams.3 Adding the 274 grams that both
defendants conceded were attributable to the conspiracy (the
75 grams found in the two searches of Equihua-Ramirez’s
property, and the 199 grams found in Guzman-Arias’s car),
the court reached a total of 374 grams. However, the court
concluded that for the remaining thirteen purchases, the jury
could only speculate as to how many times Equihua-Ramirez
purchased one, two, or three ounces. Therefore, the court
concluded that the only amount that the jury could have found
without engaging in speculation was the least of these, as it
was certain that Equihua-Ramirez purchased at least one
ounce in each of the thirteen transactions. Thus, taking
Equihua-Ramirez’s testimony and physical evidence alone,
the court concluded that the jury could have found beyond a
reasonable doubt that the conspiracy involved 699 grams of




  3
    It is unclear whether the district court meant pieces (25 grams) or
ounces; four ounces would be 112 grams, whereas four pieces would be
100.
14        UNITED STATES V. NAVARRETTE-AGUILAR

heroin (274 grams found, plus 100 grams admitted as the last
purchase, plus 325 grams).4

    Next, the court analyzed Burns’s testimony to determine
the quantity of heroin that the jury could have inferred
without speculation. Noting again the inconsistencies in
Burns’s testimony with regard to the frequency with which he
purchased heroin, the court turned to the phone records
showing calls between Equihua-Ramirez and Burns in order
to estimate the number of transactions between them. While
the court arrived at a number of transactions it believed was
adequately supported by the phone records and testimony, the
court observed that, again, the jury would have had to
speculate as to how much heroin was involved in each.
Nonetheless, the court concluded that the jury could have
found without speculation that Burns purchased 750 grams
from Equihua-Ramirez, based on Burns’s testimony that he
purchased “a few,” or three pieces (75 grams) per week, and
based on the assumption of a ten-week period.

    Thus, the court found that the physical and testimonial
evidence did not reach the one kilogram quantity threshold.
The court concluded, however, that Equihua-Ramirez’s and
Burns’s testimony provided the jury

         a reasonable ‘guide’ as to the total amount
         that was involved in the conspiracy. Based on
         the history of dealing from mid-March to


  4
     It is again unclear whether the court meant “pieces” or ounces in
coming to the total of 325 grams; 28 grams per ounce multiplied 13 times
is actually 364 grams, which would bring the total to 750 grams – 274
grams found, plus 112 grams (four ounces) for the last purchase, plus 13
purchases totaling 364 grams.
         UNITED STATES V. NAVARRETTE-AGUILAR                 15

       early June 2012 . . . and construing the
       evidence and inferences in the Government’s
       favor, the jury could have made a reasonable,
       non-speculative inference that Defendants
       must have agreed to distribute as much heroin
       as they could and that the distribution would
       have continued in a similar fashion.

That is, the court concluded that the evidence in the record
established a pattern of transactions that would have allowed
the jury to infer a preexisting agreement to distribute at least
a kilogram of heroin.

    Count One carried a mandatory minimum of twenty
years, due to Navarrette’s prior conviction and the jury’s
special finding. Count Two carried no mandatory minimum,
and Count Four carried a mandatory minimum of ten years.
On the basis of the jury’s quantity finding, as well as an
increase of three levels for Navarrette’s role in the
conspiracy, and after subtracting two levels for an anticipated
change in the U.S. Sentencing Guidelines, the court
calculated a base offense level of thirty-three. After
considering Navarrette’s criminal history, the court calculated
the guideline range for each count as 168–210 months, before
taking into account the mandatory minimum on Count One.
The court then sentenced Navarrette to 240 months on each
count of conviction (the mandatory minimum on Count One
due to the the one kilogram quantity), to run concurrently,
and to a 10-year term of supervised release following his
incarceration. The court used the same base offense level in
imposing the sentences on each count.
16       UNITED STATES V. NAVARRETTE-AGUILAR

                              II.

A. Standard of Review and Jurisdiction

    Both with respect to his sentence and his conviction,
Navarrette appeals a final judgment of a district court, and
thus we have jurisdiction under 28 U.S.C. § 1291.

     Navarrette first challenges the jury’s quantity finding for
the conspiracy to distribute and distribution charges. He does
not raise an evidence insufficiency challenge to the jury’s
verdict with respect to his convictions for any of the
substantive offenses. After Apprendi v. New Jersey, 530 U.S.
466 (2000), “[w]e . . . trea[t] drug quantity and type, which
fix the maximum sentence for a conviction, as we would any
other material fact in a criminal prosecution: it must be
charged in the indictment, submitted to the jury, subject to the
rules of evidence, and proved beyond a reasonable doubt.”
United States v. Buckland, 289 F.3d 558, 568 (9th Cir. 2002);
see also United States v. Vera, 770 F.3d 1232 (9th Cir. 2014).
The jury’s quantity finding subjected Navarrette to a twenty-
year mandatory minimum sentence, as he had previously
been convicted of a drug felony, 21 U.S.C. § 841(b)(1)(A)(i);
setting aside this finding would mean that he is no longer
subject to that mandatory minimum. Thus, the jury had to
find the one kilogram quantity beyond a reasonable doubt.

    We review a jury’s verdict and special findings for
substantial evidence, which requires that we first “construe
the evidence ‘in the light most favorable to the prosecution,’
and only then determine whether ‘any rational trier of fact
could have found the essential elements of the crime beyond
a reasonable doubt.’” Nevils, 598 F.3d at 1161 (quoting
Jackson, 443 U.S. at 319). This means that “when faced with
         UNITED STATES V. NAVARRETTE-AGUILAR                  17

a record of historical facts that supports conflicting inferences
[we] must presume . . . that the trier of fact resolved any such
conflicts in favor of the prosecution, and must defer to that
resolution.” Id. at 1164 (internal quotation marks omitted).
However, “[a]lthough we must draw all reasonable inferences
in favor of the prosecution, a ‘reasonable’ inference is one
that is supported by a chain of logic, rather than . . . mere
speculation dressed up in the guise of evidence.” Juan H. v.
Allen, 408 F.3d 1262, 1277 (9th Cir. 2005).

    Second, Navarrette challenges the district court’s
admission of evidence of his prior convictions as
impeachment evidence following the testimony of his sister,
Mini Navarrette. We review a district court’s evidentiary
rulings for abuse of discretion. United States v. Castillo,
181 F.3d 1129, 1132 (9th Cir. 1999).

B. Conspiracy Generally

    “To establish a drug conspiracy, the government must
prove: 1) an agreement to accomplish an illegal objective;
and 2) the intent to commit the underlying offense.” United
States v. Mincoff, 574 F.3d 1186, 1192 (9th Cir. 2009)
(quoting United States v. Barragan, 263 F.3d 919, 922 (9th
Cir. 2001)). The government “can prove the existence of a
conspiracy through circumstantial evidence that defendants
acted together in pursuit of a common illegal goal.” United
States v. Bishop, 1 F.3d 910, 911 (9th Cir. 1993) (citation
omitted). “Express agreement is not required; rather,
agreement may be inferred from conduct.” United States v.
Hegwood, 977 F.2d 492, 497 (9th Cir. 1992) (citation
omitted). Thus, evidence of past transactions can constitute
circumstantial evidence of a preexisting agreement, because
18       UNITED STATES V. NAVARRETTE-AGUILAR

it can be inferred that the defendants agreed to carry out those
transactions.

    Circumstantial evidence of a drug distribution conspiracy
is not limited to evidence of past completed transactions.
See, e.g., United States v. Rosales, 516 F.3d 749, 755 (9th
Cir. 2008) (considering evidence of a hydraulic press and
metal molds that could be used to produce kilogram bricks of
cocaine in determining that sufficient evidence supported a
conviction of conspiracy to distribute at least 500 grams of
cocaine). Moreover, a conspiracy conviction does not require
“the delivery, presence, or even existence of actual
contraband.” United States v. Macias-Valencia, 510 F.3d
1012, 1016 (9th Cir. 2007). But in order for the defendant to
be subject to a mandatory minimum under § 841(b)(1)(A)(i),
the government still must prove, beyond a reasonable doubt,
that an agreement to distribute one kilogram existed before
the expiration of the period alleged in the indictment. As we
explain below, the government failed to meet its burden of
proof.

C. Physical and Testimonial Evidence Presented

    Before examining whether the circumstantial evidence of
the defendants’ pattern of transactions can support the one
kilogram quantity finding, we first consider whether the
government otherwise presented sufficient evidence to
establish that amount.

    The government contends that the district court’s finding
of 750 grams, inferred from Burns’s testimony, plus the 274
grams conceded by Navarrette, exceeds one kilogram, and
thus the jury’s finding is supported by substantial evidence.
Navarrette, in turn, argues that even if the district court failed
        UNITED STATES V. NAVARRETTE-AGUILAR                 19

to add all of the 274 grams of physical evidence in reaching
the 750 gram estimate, “it is fair to assume that [the district
court] counted at least the 62 grams seized from Equihua-
Ramirez, as this amount was earmarked for Burns.” Even
adding the remaining 212 grams to the 750 grams inferred
from Burns’s testimony, the quantity still falls short of one
kilogram. Navarrette further argues that the district court
erred when it determined that the conspiracy continued for
ten weeks, because it was “undisputed that the heroin went
‘bad’ for a while during which time Burns purchased heroin
from Equihua-Ramirez only once,” and, moreover, “Equihua-
Ramirez testified that this was a substantial period during
April and May.”

    While it is true that Equihua-Ramirez testified at one
point that the period during which the heroin went bad lasted
most of April, at another point during the trial, he testified
that it lasted approximately fifteen days. Burns likewise
testified that he did not purchase heroin from Equihua-
Ramirez for a period, although he did not testify how long
that lasted. Because we must resolve all conflicting evidence
in favor of the prosecution, we will use the lower of Equihua-
Ramirez’s estimates (that is, fifteen days), and conclude that
the period in which Equihua-Ramirez and Burns conducted
their transactions spanned eight weeks, not ten (ten weeks
minus fifteen days). Using the district court’s 75 gram per
week calculation (from Burns’s testimony that he purchased
“a few” each week) the total would thus come to 600 grams.
Even adding 75 grams for the single instance in which Burns
purchased three pieces, and all of the 274 grams that
Navarrette conceded, the total amount of heroin established
would come to 949 grams. There was no evidence presented
that Equihua-Ramirez’s additional gram-level customers
would make up the difference.
20      UNITED STATES V. NAVARRETTE-AGUILAR

     Turning to Equihua-Ramirez’s testimony, even if we
attempted to determine the quantity of heroin from his
testimony regarding his sales to Burns (instead of the 699
grams based on the number of Equihua-Ramirez’s purchases),
it still would not reach a kilogram. Equihua-Ramirez testified
that Burns bought “sometimes two, sometimes three” pieces
a week from him (fifty or seventy-five grams), but also
testified that Burns stopped buying from him for a period.
Equihua-Ramirez also testified repeatedly that he only sold
Burns three pieces on one single occasion. Thus, a relatively
liberal calculation based on his sales to Burns, as well as his
admitted four-ounce buy (which risks double-counting, since
some of that could have been sold to Burns) and the 200
grams found on Guzman-Arias (his last order) would still not
total a kilogram: 50 grams multiplied by 8 weeks (two pieces
per week, and not counting the period the heroin went bad)
plus 75 grams (the single three piece buy) plus 112 grams
(the four ounce order) plus 200 grams (the final controlled
buy) totals 787 grams.

    The district court did not attempt to determine an average
amount of heroin distributed either from Burns’s testimony or
from Equihua-Ramirez’s testimony, instead relying on the
least amount that either defendant testified was his minimum
sale or purchase. We have previously approved the
“multiplier method,” for approximating drug quantity “by
determining a daily or weekly quantity, selecting a time
period over which it is more likely than not that the defendant
was dealing in that quantity and multiplying these two factors
together,” United States v. Culps, 300 F.3d 1069, 1077 (9th
Cir. 2002). However, we have done so only in the sentencing
context, in which the government was required to prove
quantity by a preponderance of the evidence for sentencing
purposes, and not, as here, where the factual issue had to be
          UNITED STATES V. NAVARRETTE-AGUILAR                        21

proved beyond a reasonable doubt. Under the Jackson
standard, we are obliged to construe the evidence of drug
quantity adduced at trial “in the light most favorable to the
prosecution,” and only after viewing the evidence in this
light, determine whether, resolving all conflicting inferences
in favor of the prosecution, “any rational trier of fact could
have found” the one kilogram quantity “beyond a reasonable
doubt.” 443 U.S. at 319. Jackson v. Virginia, 443 U.S. at
319. Applying the Jackson standard, we conclude that the
district court did not err in declining to apply the multiplier
method given the facts of this case.

    We further conclude that the district court did not err in
disregarding the circumstantial evidence of the secret storage
compartment in Navarrette’s vehicle, capable of holding 30
pounds of drugs. The government offered no evidence that
the storage compartment was used to transport heroin, as
opposed to any other kind of contraband, or that Navarrette
ever used the compartment. We also note that the
drug-sniffing dog did not alert to the compartment during the
search.5

    Therefore, as did the district court, we conclude that the
testimonial and physical evidence cannot support a finding of
one kilogram.


   5
     While we have stated that a defendant’s mere access to equipment
capable of producing a kilogram of cocaine “supports the jury’s verdict
that it was reasonably foreseeable that the conspiracy involved 500 grams
or more of cocaine,” Rosales, 516 F.3d at 755, the government did not
raise this argument on appeal, and therefore we do not address it here.
“Our circuit has repeatedly admonished that we cannot manufacture
arguments for an appellant.” Ind. Towers of Wash. v. Washington,
350 F.3d 925, 929 (9th Cir. 2003) (quoting Devereaux v. Abbey, 263 F.3d
1070, 1082 (9th Cir. 2001)).
22       UNITED STATES V. NAVARRETTE-AGUILAR

D. The Pattern of Heroin Transactions

    We turn to the district court’s conclusion that the
defendants’ pattern of transactions constituted circumstantial
evidence, such that “the jury could have made a reasonable,
non-speculative inference that Defendants must have agreed
to distribute as much heroin as they could and that the
distribution would have continued in a similar fashion.”

    Even if some hypothetical pattern of transactions were
consistent and clear enough to infer a preexisting agreement
to surpass a certain quantity, such is not the pattern before us.
While the testimony of Equihua-Ramirez and Burns could
prove repeated transactions over a period of eight weeks, the
testimony did not show any consistency in those transactions,
either with respect to amount or to frequency, from which a
jury could reasonably infer an agreement to distribute a
kilogram of heroin. This conclusion is underscored by the
vague and equivocal nature of the testimony itself. Both
witnesses at points contradicted themselves, and Burns
repeatedly indicated that his memory was unreliable.

    Even construing the evidence in the light most favorable
to the prosecution, the purchases in this case appear to have
been ad hoc, and dependent on the level of demand at any
given moment. The evidence showed that Equihua-Ramirez
bought his supply of heroin from Navarrette only once he had
sold the amount he had previously purchased; that Burns was
Equihua-Ramirez’s biggest customer; that Burns only
purchased heroin when there was sufficient demand; that
demand was “different all the time”; and that there was a
period of approximately two weeks out of a total period of ten
weeks in which the heroin “went bad,” and Burns did not
purchase any heroin.
         UNITED STATES V. NAVARRETTE-AGUILAR                  23

    Moreover, the testimony given at trial revealed that the
whole arrangement was temporary and unstable. During the
period alleged in the indictment, Equihua-Ramirez was
effectively subbing for his friend. He testified that he had no
intention of continuing once his friend returned, and, in fact,
that he became so frustrated with the bad heroin that he
considered quitting. Similarly, Burns repeatedly testified that
he intended to quit selling heroin. In sum, it would be
speculative to infer that the defendants agreed to any future
transactions such that they would reach the one kilogram
mark. Speculation cannot constitute substantial evidence.
See Juan H., 408 F.3d at 1277.

    Our conclusion is further supported by the Fourth
Circuit’s holding in United States v. Hickman, 626 F.3d 756
(4th Cir. 2010). In that case, the court held that substantial
evidence did not support a conviction for conspiracy to
distribute one kilogram of heroin where the past transactions
and future, expressly agreed-upon transactions amounted to
a maximum of 836 grams. Id. at 766. In Hickman, as in this
case, the government argued that the jury could conclude that
the transactions proven were part of an “ongoing course of
business.” Id. at 768. The government in that case further
argued that “[it was] clear that . . . [the defendant] would have
continued” to distribute heroin. Id. The Hickman court
disagreed. It concluded that such a finding would come
perilously close to impermissibly convicting the defendant of
“hypothesized future bad acts,” and, moreover, that “[w]here
no evidence exists to guide the trier of fact in determining the
outer scope of a conspiracy, the trier may not simply guess at
the magnitude or frequency of unknown criminal activity.”
Id. at 768–69.
24       UNITED STATES V. NAVARRETTE-AGUILAR

    In this case, the district court attempted to distinguish
Hickman. In Hickman, the defendants agreed to or actually
undertook three transactions, whereas in this case the number
is at least ten. Therefore, the district court concluded that,
unlike in Hickman, here there was sufficient evidence to
“guide” the jury “as to the total amount that was involved in
the conspiracy,” because there were “multiple purchases and
multiple sales and thus, there were more than a ‘limited
number of actual transactions.’” But though the evidence
here showed more transactions than in Hickman, Hickman is
not so easily distinguishable. In Hickman, the evidence
supported a finding that the defendants had distributed a
maximum of 836 grams over a period of four months, which
is not much different than the up to 750 grams over a period
of three months (according to the district court’s calculations)
in this case. And here, like in Hickman, the argument that the
co-conspirators would have distributed one kilogram if it had
not been interrupted potentially allows a quantity finding to
stand upon what Navarrette “would have continued to do[,]
which, to the extent these hypothesized future bad acts were
not captured by an agreement within the charged period, is
clearly improper.” Hickman, 626 F.3d at 768 (internal
quotation marks omitted). Such a theory impermissibly
“invites the jury to speculate as to the amount of heroin
involved in the conspiracy.” Id.

    The government agrees that, should we conclude that
substantial evidence does not support the jury’s verdict on the
one kilogram quantity special finding, the error was not
harmless and re-sentencing would be appropriate. While the
special finding only resulted in a mandatory minimum
sentence on Count One, the district court imposed an identical
sentence on all counts. It is clear that the district court used
this twenty-year sentence as the “starting point and the initial
          UNITED STATES V. NAVARRETTE-AGUILAR                           25

benchmark,” Kimbrough v. United States, 552 U.S. 85, 108
(2007) (quoting Gall v. United States, 552 U.S. 38, 49
(2007)), and that, had the district court sentenced Navarrette
absent the special finding and mandatory minimum, “it may
have arrived at a different sentence,” see United States v.
Munoz-Camarena, 631 F.3d 1028, 1031 (9th Cir. 2011).
Therefore, we reverse the jury’s quantity finding, vacate
Navarrette’s sentence on all counts, and remand for re-
sentencing.6

                                   III.

    Navarrette challenges his conspiracy and substantive
count convictions on the ground that the district court abused
its discretion when it permitted the government to ask his
sister, defense witness Mini Navarrette, about his prior
Washington state convictions for drug trafficking and escape.

     The district court had originally granted a pre-trial motion
in limine to exclude these convictions as overly prejudicial.
However, on cross examination, Mini Navarrette stated that
her brother could not drive because he did not have a license,
and that “[she knew] that [her] brother did not do any drugs
or anything.” The government argued that she had opened
the door to impeachment, because she knew that Navarrette


   6
     Because Navarrette’s evidence insufficiency claim is limited to the
jury’s quantity finding, we vacate his sentence, but we do not reverse the
underlying conspiracy conviction under 21 U.S.C. § 841(a). As we have
explained, “[t]he tainted drug quantity verdict does not affect the validity
of the underlying conspiracy conviction because drug quantity was not an
element of the charged conspiracy offense; rather, it . . . had to be
submitted to a jury and proved beyond a reasonable doubt for the purposes
of sentencing alone.” United States v. Vera, 770 F.3d 1232, 1249 (9th Cir.
2014).
26      UNITED STATES V. NAVARRETTE-AGUILAR

could not drive because he was afraid that he would be pulled
over and the outstanding warrant stemming from his escape
discovered, and because she knew that he previously had
been convicted and imprisoned. Navarrette objected, but the
court allowed the government to question Mini Navarrette
about her brother’s prior convictions.

    On cross-examination, a defense witness opens the door
to impeachment by the prosecution if she “truly volunteer[s]”
the impeachable testimony. Id. at 1134 n.1. Here, the
government directly asked Mini Navarrette why her brother
was unable to drive a car. The record does not support the
government’s contention that Ms. Navarrette volunteered that
her brother never used the car that was in her name and her
sister-in-law’s name. But, Ms. Navarrette opened the door to
impeachment later in her testimony, when she volunteered
that she knew that her brother was not involved in drugs. Ms.
Navarrette knew that her brother had previously been
convicted and imprisoned, and had escaped. While it is
possible that she did not know the exact nature of the
conviction, the district court did not abuse its discretion in
allowing the government to ask her about her brother’s prior
convictions.

    Moreover, even if the district court did abuse its
discretion, the error was harmless. As the government
argues, Navarrette’s conviction was supported by phone
records tying him to Equihua-Ramirez, as well as by
Equihua-Ramirez’s testimony that Navarrette’s voice on a
recorded call was the voice of his supplier, “Califas.” Ms.
Navarrette’s testimony, intended to support the defense
        UNITED STATES V. NAVARRETTE-AGUILAR                 27

theory that Navarrette had no involvement in the conspiracy,
could not have overcome the weight of this evidence.
Accordingly, we affirm the district court’s evidentiary ruling.

    AFFIRMED in part, REVERSED in part, VACATED
in part, and REMANDED for re-sentencing.
