                                RECOMMENDED FOR PUBLICATION
                                Pursuant to Sixth Circuit I.O.P. 32.1(b)
                                       File Name: 20a0262p.06

                    UNITED STATES COURT OF APPEALS
                                  FOR THE SIXTH CIRCUIT



 UNITED STATES OF AMERICA,                                   ┐
                                    Plaintiff-Appellee,      │
                                                             │
                                                              >        No. 19-3094
        v.                                                   │
                                                             │
                                                             │
 RUSSELL DAVIS,                                              │
                                 Defendant-Appellant.        │
                                                             ┘

                          Appeal from the United States District Court
                         for the Northern District of Ohio at Cleveland.
                  No. 1:16-cr-00260-1—Christopher A. Boyko, District Judge.

                                     Argued: June 17, 2020

                              Decided and Filed: August 14, 2020

               Before: GILMAN, KETHLEDGE, and MURPHY, Circuit Judges.
                                 _________________

                                            COUNSEL

ARGUED: Dennis C. Belli, Columbus, Ohio, for Appellant. Matthew B. Kall, UNITED
STATES ATTORNEY’S OFFICE, Cleveland, Ohio, for Appellee. ON BRIEF: Dennis C.
Belli, Columbus, Ohio, for Appellant. Matthew B. Kall, UNITED STATES ATTORNEY’S
OFFICE, Cleveland, Ohio, for Appellee.
                                      _________________

                                             OPINION
                                      _________________

       MURPHY, Circuit Judge. Federal drug laws impose enhanced sentences if a “death
results” from the use of the drugs that a defendant distributes. This “death-results” enhancement
led the district court in this case to impose a life sentence on Russell Davis. Davis sold drugs
that were later shared with Jacob Castro-White, who tragically died of a fentanyl overdose.
 No. 19-3094                          United States v. Davis                              Page 2


Davis argues that the enhancement does not apply because he did not sell drugs directly to
Castro-White.    The enhancement’s text, however, does not require such a buyer-seller
relationship with the victim. We also reject Davis’s other evidentiary and instructional claims.

       At the same time, Davis raises a valid challenge to the warrant that allowed the police to
search his home and seize his cellphone. The government now concedes that the affidavit
supporting this warrant lacked probable cause. But the government asserts that the affiant gave
additional unrecorded oral testimony to establish probable cause in front of the state magistrate
who issued the warrant. The Fourth Amendment does not mandate recorded testimony, so we
will allow the government to offer evidence of this additional testimony in an evidentiary hearing
on remand. We thus deny most of Davis’s claims, but remand for limited proceedings on this
Fourth Amendment issue.

                                                I

       Jacob Castro-White was an avid bodybuilder living in Lorain, Ohio. Many of the 23-
year-old’s friends and family knew that he used steroids and protein powders. Some knew that
he used other substances, like thyroid medications, to further enhance his appearance. And some
knew that he smoked marijuana and used cocaine. But Castro-White concealed his abuse of
opiates from all but a few friends. His mother was thus blindsided when she discovered her
young son dead in his bedroom on the morning of March 7, 2016.

       A first responder observed drug paraphernalia in Castro-White’s room: needles, a spoon,
and a silver wrapper containing a white powdered substance. Castro-White also had a “foam
cone” covering his mouth, an all-too-common sign of an opiate overdose. The responder called
Detective Ernest Sivert of the Lorain Police Department to the scene. Sivert retraced Castro-
White’s final hours through cellphone data and interviews with friends—including, most
importantly, Zaharias (“Harry”) Karaplis and Corey Stock.

       Sivert’s investigation identified Russell (“Red”) Davis as the dealer who sold the drugs
that killed Castro-White. The government indicted Davis on two drug counts. 21 U.S.C.
§ 841(a)(1). The first charged Davis with distributing a substance containing fentanyl, and the
second charged him with possessing with intent to distribute a mixture containing cocaine. The
 No. 19-3094                          United States v. Davis                              Page 3


indictment alleged that Davis should receive an increased sentence on the first count because a
death had “result[ed] from” the fentanyl that he distributed. Id. § 841(b)(1)(C). Davis pleaded
guilty to the cocaine charge but stood trial on the fentanyl charge (with its increased
punishment).

       At trial, the parties did not dispute that Davis was a drug dealer. His counsel conceded
that the evidence was “overwhelming” that Davis sold heroin to Stock and Karaplis. Both men
testified that they often bought heroin from Davis before Castro-White’s death. The parties
instead disputed whether Davis sold the specific drugs that killed Castro-White on March 7. The
government argued that Davis sold these drugs to Karaplis just after midnight. Davis argued that
the drugs came from someone else, such as Stock’s friend Erika Matus.

       The government offered a simple theme: “Follow the phones.” It relied on data from the
cellphones of Castro-White, Karaplis, Stock, and Davis. The police recovered text messages
sent to and from Castro-White’s phone from March 5 to 7 through a subpoena to Verizon. They
also seized Davis’s phone during a search of his home and were able to retrieve his call logs and
text messages. Subpoenas to Karaplis’s and Stock’s wireless carriers turned up their phones’ toll
records and cell-site data. Toll records memorialized “the calls and text messages placed to and
from” the phones without disclosing the actual content of any calls or texts. Cell-site data
identified the phones’ general locations at given points in time.

       The government’s evidence showed that Castro-White started the evening of March 6
watching a movie with his girlfriend. A little before 10:00 p.m., he visited a friend’s home and
smoked marijuana. He also began texting Stock about a heroin buy, asking him if he was
“grabbing at all.” Stock replied that he had already done so. After some back-and-forth, Stock
told Castro-White: “I can ask Erika if they have some extra to sell but you probably won’t feel it
at all, I did a two point shot over there house yesterday didn’t feel a th[ing].” Castro-White
declined: “Yeah I’ll just wait for next time with red” (Davis’s nickname). Stock then said, “I’ll
let you know if I go again tonight or if someone else calls me.” At 10:46 p.m., Castro-White
responded: “Ok thank you.” That was the last Stock heard from him.
 No. 19-3094                         United States v. Davis                             Page 4


       Castro-White and Karaplis began texting less than an hour later about purchasing heroin
from Davis. Castro-White asked Karaplis if he was planning to buy heroin, and the two spoke
on the phone. After they hung up, Karaplis texted Davis: “Hey man can I get for me dude.”
Davis did not respond, so Karaplis called him several times. Davis finally returned his call at
12:06 a.m. Karaplis said they discussed a heroin buy. At 12:15, he texted Castro-White that
Davis had been “asleep” and that Castro-White should pick Karaplis up quickly because Davis
“might fall back asleep.” Castro-White responded: “On way.” At 12:18, he texted Karaplis:
“Outside.” Davis had asked for cigarettes, so they stopped at a gas station on the way. Karaplis
called Davis at 12:34 and said he was outside. Cell-site data confirmed that Karaplis’s and
Castro-White’s phones moved from a location near Karaplis’s home to one near Davis’s.
Karaplis walked from Castro-White’s car to Davis’s house, gave Davis $50 and a pack of
Newports, and took what he thought was heroin.

       Karaplis and Castro-White drove to Castro-White’s house to split the drugs. Castro-
White took a “shot” from his portion, with some left over. They then left for Karaplis’s home.
On arriving, Karaplis also took a shot in his usual amount. He “almost fell out of [his] chair,”
and Castro-White asked if he was okay. The next thing Karaplis remembered, he “woke up on
the ground soaking wet and [Castro-White] was gone.” Karaplis frantically called and texted
Castro-White beginning at 2:51 a.m. He called Castro-White 11 times between 2:51 and 3:04
and texted him to “please call me asap.” There was no answer. Karaplis began calling again at
6:41 a.m., trying Castro-White over 20 times between 8 and 9 a.m. Karaplis was worried about
Castro-White because his shot had been “the strongest thing [he had] ever taken.”

       In the weeks after Castro-White’s death, Stock told Davis that the drugs he had sold
Karaplis had killed one of their friends. According to Stock, Davis responded: “Okay, I’m not
too worried about that because I never sold anything to that person. I do not know him. I just
sold to you and Harry.”

       While Castro-White and Karaplis had thought they bought heroin, the government’s
evidence showed that Castro-White died of an overdose from fentanyl (a much stronger drug). A
toxicologist called the “high” amount of fentanyl in Castro-White’s blood “within that area of
 No. 19-3094                           United States v. Davis                             Page 5


concentrations that have been detected in deaths due to fentanyl.” And the Lorain County
Coroner opined that Castro-White died of a fentanyl overdose between 1:00 and 2:00 a.m.

        In his defense, Davis offered evidence to suggest that someone else (possibly Matus) sold
the fatal drugs. He pointed to a text message on March 7 at 11:21 a.m. in which he told Karaplis
“Was sleep.” Because this text came after Karaplis’s text from the night before (“Hey man can I
get for me dude”), Davis argued that it showed that the two had not connected and that he was
explaining why he did not respond. (For her part, Matus denied ever selling drugs to Castro-
White or Karaplis and testified that she did not know them well.)

        The jury returned a guilty verdict on the fentanyl count and the death-results
enhancement. Because Davis had a prior conviction for a felony drug offense, the district court
imposed a mandatory life sentence to run concurrent to a 360-month sentence on the other
cocaine count.

                                                 II

        Davis raises six challenges on appeal. He argues at the outset that the government
wrongly imposed the death-results enhancement for three reasons. He next raises an evidentiary
claim against the coroner’s expert opinion and an instructional claim against the district court’s
response to a jury question. He lastly asserts Fourth Amendment claims against the search of his
home.

                                 A. Death-Results Enhancement

        Davis’s first three arguments challenge his life sentence. Federal law (in particular,
21 U.S.C. § 841(a)) prohibits the knowing distribution of a controlled substance. Section 841(b)
then lists different sentences for those “who violate[] subsection (a)” depending on the drug type
and quantity. Id. § 841(b). Section 841(b)(1)(C) lists the sentences for fentanyl, a controlled
substance in Schedule II. See United States v. Jeffries, 958 F.3d 517, 519 (6th Cir. 2020). This
subparagraph imposes a mandatory life sentence if a defendant with a prior felony drug
conviction distributes an illegal substance and death results from its use:
 No. 19-3094                          United States v. Davis                               Page 6


       If any person commits such a violation after a prior conviction for a felony drug
       offense has become final, such person shall be sentenced to a term of
       imprisonment of not more than 30 years and if death or serious bodily injury
       results from the use of such substance shall be sentenced to life imprisonment, a
       fine not to exceed the greater of twice that authorized in accordance with the
       provisions of Title 18 or $2,000,000 if the defendant is an individual or
       $10,000,000 if the defendant is other than an individual, or both.

21 U.S.C. § 841(b)(1)(C) (emphasis added).

       Davis asserts (1) that the district court improperly instructed the jury about this
enhancement, (2) that the evidence was insufficient to convict him of it, and (3) that the evidence
amounted to a “constructive amendment” of his indictment. These three arguments all share the
same legal premise about the proper interpretation of this enhancement. We thus begin with
Davis’s general legal interpretation and then turn to his specific arguments.

                                                 1

       In Davis’s view, a defendant cannot receive the death-results enhancement unless the
defendant directly delivered the drug to the person who died or provided the drug to that victim
through a coconspirator. Because Davis did not sell drugs directly to Castro-White or conspire
with Karaplis, his argument goes, his conduct should not have triggered the enhancement. Davis
misreads § 841(b)(1)(C). The statute requires the government to prove only that the specific
drug underlying a defendant’s violation of § 841(a) is the same drug that was the but-for cause of
the victim’s death. This reading follows from both text and precedent.

       We begin with the text’s ordinary meaning. Burrage v. United States, 571 U.S. 204,
210–11 (2014). By its terms, the enhancement applies if there is a “death or serious bodily
injury” and this death or serious bodily injury “results from” the “use of such substance” (the
drug that the defendant distributed in violation of § 841(a)). 21 U.S.C. § 841(b)(1)(C). Notably
absent: any requirement that the defendant directly sell the fatal drugs to the victim who died or
conspire with the person who did. The text requires only that the defendant have a connection to
the death-causing drugs, not to the deceased person. That is, the drugs supporting a defendant’s
§ 841(a) conviction must be the same drugs that caused death. If so, the enhancement applies
whether or not the defendant has a connection to (or even knowledge of) the person who died.
 No. 19-3094                            United States v. Davis                              Page 7


       Consider a defendant who runs a cartel that manufactures large amounts of fentanyl. The
defendant’s “manufacture” of that fentanyl would violate § 841(a)(1). But the defendant might
sell this fentanyl to wholesalers, not end users. And the wholesalers might resell it through a
diverse chain ending with small dealers.        If the government proves that the fentanyl the
defendant manufactured is the same fentanyl that caused a user’s death, § 841(b)(1)(C)’s text
triggers this enhancement even if the defendant did not know the dealer or the decedent. Any
other reading would require us to add words to the statute that are not there.

       Precedent confirms this view. In Burrage, the Supreme Court held that the phrase
“results from” requires a but-for causal connection between the victim’s use of the drug and the
victim’s death. 571 U.S. at 211–14. The Court nowhere suggested that the government must
show, in addition, a close connection between the distribution of the drug and that death. To the
contrary, Burrage emphasized the need “to apply the statute as it is written[.]” Id. at 218. We
expanded on this point in Jeffries. That case rejected the argument that the enhancement
includes a proximate-causation element requiring proof that the victim’s death was the
foreseeable result of the defendant’s conduct.         958 F.3d at 520–21.       As we observed,
§ 841(b)(1)(C) “does not speak to the defendant’s conduct or the general causal connection
between § 841(a)(1) and the death.” Id. at 521. Rather, the text asks only whether the victim’s
use of the drug caused the death. Id.

       Davis’s response does not change things. He offers no reading of § 841(b)(1)(C)’s text
that supports his view that a defendant must deliver the drug directly to the victim or be linked to
the victim through coconspirators. Instead, he bases this view on two decisions—United States
v. Swiney, 203 F.3d 397 (6th Cir. 2000), and United States v. Hamm, 952 F.3d 728 (6th Cir.
2020). Swiney explained how the enhancement applies to defendants in a drug conspiracy under
21 U.S.C. § 846. 203 F.3d at 401–06. It relied on a Sentencing Guideline to hold that a
coconspirator must be “part of the distribution chain that [led] to [the victim’s] death.” Id. at
406. Hamm held that this rule extends to coconspirators convicted of a substantive offense under
§ 841(a) (not a conspiracy offense under § 846) if the theory of the coconspirators’ substantive
liability is that they conspired with the person who committed the offense. 952 F.3d at 744–47.
 No. 19-3094                          United States v. Davis                               Page 8


       Neither decision applies here. Davis was not charged with a conspiracy under § 846. See
Swiney, 203 F.3d at 400. Nor was he held liable for his § 841(a) offense on a conspiracy theory.
See Hamm, 952 F.3d at 744. And nothing in Swiney or Hamm suggests that those decisions
apply to a case involving a substantive charge under § 841(a) not predicated on a conspiracy.
The decisions are thus “irrelevant here because [Davis] is not being held responsible for someone
else’s actions based on his status as a co-conspirator, but is being punished for his own actions.”
United States v. Atkins, 289 F. App’x 872, 877 (6th Cir. 2008); see also United States v.
Carbajal, 290 F.3d 277, 284–85 (5th Cir. 2002); United States v. Soler, 275 F.3d 146, 152 (1st
Cir. 2002).

                                                2

       Under this reading of the death-results enhancement, Davis’s jury-instruction,
sufficiency-of-the-evidence, and constructive-amendment claims all fail.

       a. Jury Instructions. Davis argues that the district court erred by failing to instruct the
jury that he could be liable only if he distributed the fatal drugs directly to the decedent or
conspired with the person who did. As explained, this view misstates the law.

       b. Sufficiency of the Evidence. Davis also claims that the evidence could not support this
enhancement on the same ground—because he did not sell the drugs directly to Castro-White or
conspire with Karaplis. Yet, under a proper view of the law, sufficient evidence existed. For a
sufficiency challenge, we ask “whether, after viewing the evidence in the light most favorable to
the prosecution, any rational trier of fact could have found the essential elements of the crime
beyond a reasonable doubt.” Hamm, 952 F.3d at 736 (citation omitted).

       Here, a rational jury could have found that the drugs Castro-White used on March 7 were
the drugs that Davis distributed to Karaplis, in violation of § 841(a). Karaplis testified that he
got the drugs from Davis and split them with Castro-White. And text messages, call records, and
cell-site data corroborated this testimony. A rational jury next could have found that Castro-
White’s death “result[ed] from [his] use of” Davis’s drugs. 21 U.S.C. § 841(b)(1)(C). Based on
the fentanyl in Castro-White’s blood, the coroner opined that “the use of fentanyl was the but for
cause of his death.” Cf. Hamm, 952 F.3d at 737–38. The enhancement requires nothing more.
 No. 19-3094                          United States v. Davis                               Page 9


       In response, Davis cites United States v. Ewing, 749 F. App’x 317 (6th Cir. 2018), which
found insufficient evidence for this enhancement. Id. at 328–29. The defendant had sold the
victim heroin laced with fentanyl, but only fentanyl (not heroin) was in the victim’s blood. Id.
So the defendant’s drugs did not cause the victim’s death. Id. Davis argues that his case is like
Ewing because Karaplis testified that Davis sold him heroin, but Castro-White died from
fentanyl.   Yet a rational jury could find that Karaplis thought he was getting heroin but
unknowingly received the much stronger fentanyl. Karaplis and Stock suspected Davis might be
selling fentanyl because of the potency of his drugs. A scientist who sees “thousands of cases a
year” also testified that she cannot visually distinguish the two drugs. Lastly, ample evidence
suggests that Castro-White used Davis’s opiates (and not others) just before his death.

       c. Constructive Amendment. Davis lastly argues that the evidence and jury instructions
differed from the indictment’s allegations to such an extent that his trial resulted in a
“constructive amendment” of his indictment. Davis did not raise this objection in the district
court, so we review it for plain error. United States v. Budd, 496 F.3d 517, 528 (6th Cir. 2007).

       Under the Fifth Amendment, “[n]o person shall be held to answer for a capital, or
otherwise infamous crime, unless on a presentment or indictment of a Grand Jury[.]” U.S.
Const. amend. V. In Stirone v. United States, 361 U.S. 212 (1960), the Court held that this
provision bars the government from charging the defendant of one crime in an indictment and
convicting the defendant of another crime at trial. Id. at 217–19. The Stirone indictment had
charged a Hobbs Act violation for interfering with the interstate commerce in one commodity:
sand. Id. at 213. Yet the jury instructions allowed the jury to convict the defendant for
interfering with the interstate commerce in another commodity: steel. Id. at 214. The Court held
that interference with commerce is an “essential element[]” of the crime and that the indictment
alleged only one type of interference, so the “conviction must rest upon that charge and not
another[.]” Id. at 218.

       Courts have long called Stirone a case about a “constructive amendment” of an
indictment (it did not use the phrase) and have distinguished such an amendment from a mere
“variance” between the trial and indictment. See United States v. Beeler, 587 F.2d 340, 342 (6th
Cir. 1978) (adopting Gaither v. United States, 413 F.2d 1061 (D.C. Cir. 1969)); United States v.
 No. 19-3094                         United States v. Davis                            Page 10


Withers, 960 F.3d 922, 935 (7th Cir. 2020) (Easterbrook, J., concurring) (retracing history).
A “constructive amendment” occurs if the instructions and evidence “so modify essential
elements of the offense charged that there is a substantial likelihood the defendant [was]
convicted of an offense other than that charged in the indictment.” United States v. Warshak,
631 F.3d 266, 313 (6th Cir. 2010) (citation omitted). A mere variance occurs if the evidence
“proves facts materially different from those alleged in the indictment.” Budd, 496 F.3d at 521
(citation omitted).

       These definitions draw a “blurry,” “sketchy,” or “shadowy” line between an amendment
and a variance. See United States v. Beasley, 583 F.3d 384, 389 (6th Cir. 2009); United States v.
Chilingirian, 280 F.3d 704, 712 (6th Cir. 2002); United States v. Hathaway, 798 F.2d 902, 910
(6th Cir. 1986) (citation omitted). Yet the category of an alleged divergence between the
indictment and trial matters greatly. A constructive amendment is “per se prejudicial,” so we
must reverse without a showing that the difference between the indictment and trial prejudiced
the defendant. United States v. Hynes, 467 F.3d 951, 962 (6th Cir. 2006) (citation omitted).
A variance, on the other hand, must “affect[] a substantial right,” so we may reverse only if the
defendant proves prejudice. United States v. Mize, 814 F.3d 401, 409 (6th Cir. 2016) (citation
omitted).

       What is Davis’s constructive-amendment theory? He again relies on his mistaken view
of the law. The indictment stated that Davis “distributed to” Castro-White:

       On or about March 7, 2016, in Lorain, Ohio, IND-1, a person whose identity is
       known to the Grand Jury, did fatally ingest and overdose on a controlled
       substance, namely fentanyl, which RUSSELL DAVIS, aka “Red,” had distributed
       to IND-1. As a result of RUSSELL DAVIS’ distribution of fentanyl alleged in
       Count 1, death did result from the use of fentanyl, a Schedule II controlled
       substance.

Indictment, R.1, PageID #1–2 (emphasis added). The jury instructions, however, required the
jury to find only that Castro-White “died as a consequence of his use of the drugs” that Davis
sold, without requiring a finding that Davis himself distributed the drugs to Castro-White. The
evidence likewise showed that Davis distributed the drugs to Karaplis.
 No. 19-3094                         United States v. Davis                              Page 11


       This difference did not create a constructive amendment. Davis’s theory turns on his
view that the enhancement required, as an essential element, that the jury find he sold the drugs
directly to Castro-White. See Stirone, 361 U.S. at 218. It did not. The enhancement required
the jury to find only that fentanyl caused Castro-White’s death and that this fentanyl had been
distributed by Davis. For those “essential elements,” the indictment’s facts matched those at
trial. See id. And even if the indictment’s language that Davis “distributed to” Castro-White
could be read to mean directly to him, the language was “surplusage.” Id.; Hathaway, 798 F.2d
at 911. The indictment did not thereby charge a different offense—as it would have if, say, it
identified a decedent other than Castro-White. Davis thus has not shown that he received an
enhanced sentence for conduct “other than that charged in the indictment.” Warshak, 631 F.3d at
313 (citation omitted).

       Davis does not even assert the fallback position that a variance occurred. That is for
good reason. He could not show prejudice from the difference between the indictment and trial.
He does not argue that he lacked notice of the government’s factual theory. See Beasley,
583 F.3d at 392. He also “does not assert that he was unable to adequately prepare his defense”
or that any difference could expose him to the risk of “future prosecutions based upon the same
conduct.” Id.

       All told, the district court properly imposed the death-results enhancement in this case.

                                     B. Coroner Testimony

       Davis next argues that the district court wrongly allowed the coroner, Dr. Stephen Evans,
to give expert testimony that fentanyl caused Castro-White’s death. Davis asserts that Evans’s
failure to order an autopsy rendered his opinion inadmissible under Daubert v. Merrell Dow
Pharmaceuticals, Inc., 509 U.S. 579 (1993). Davis did not object at trial, so we again review his
claim for plain error. United States v. Johnson, 488 F.3d 690, 697 (6th Cir. 2007).

       Under Daubert, a district court must “ensur[e] that an expert’s testimony both rests on a
reliable foundation and is relevant to the task at hand.” 509 U.S. at 597. Federal Rule of
Evidence 702 codifies these standards, imposing four requirements that likewise seek to ensure
 No. 19-3094                          United States v. Davis                              Page 12


that “scientific testimony” is “both ‘relevant’ and ‘reliable.’” Madej v. Maiden, 951 F.3d 364,
369 (6th Cir. 2020) (citation omitted); Fed. R. Evid. 702(a)–(d).

       Here, there is no dispute that Dr. Evans’s testimony was relevant because the government
needed to prove that Davis’s drugs caused Castro-White’s death. See Burrage, 571 U.S. at 218–
19. This case instead concerns reliability. We have held that experts who give medical-
causation opinions may meet Daubert’s reliability rules through a “differential diagnosis” or
“differential etiology.” Tamraz v. Lincoln Elec. Co., 620 F.3d 665, 674 (6th Cir. 2010). That
method seeks to “rule in” potential causes of a condition and “rule out” other causes. Id. We
have viewed a differential diagnosis as sufficiently reliable when a doctor: “(1) objectively
ascertains, to the extent possible, the nature of the patient’s injury”; “(2) ‘rules in’ one or more
causes of the injury using a valid methodology”; and “(3) engages in ‘standard diagnostic
techniques by which doctors normally rule out alternative causes’ to reach a conclusion as to
which cause is most likely.” Best v. Lowe’s Home Ctrs., Inc., 563 F.3d 171, 179 (6th Cir. 2009)
(citation omitted).

       When reviewed for plain error, Dr. Evans’s opinion meets this test. Davis does not
dispute that Dr. Evans’s opinion satisfied our framework’s first two elements.           Dr. Evans
explained that his opinion that fentanyl caused Castro-White’s death rested on his review of the
scene, the body’s condition, the police reports, and the lab reports. His investigation of the scene
revealed drug paraphernalia that tested positive for heroin and fentanyl. And Castro-White’s
mouth had a “foam cone” typical of narcotics overdoses. Dr. Evans also ordered blood and urine
screens; the urine screen tested positive for opiates and marijuana, while the blood screen
showed a fentanyl level that was “three times the highest therapeutic dose[.]”

       Davis instead focuses on the third differential-diagnosis element.        He says that Dr.
Evans’s failure to order an autopsy means that he did not engage in “standard diagnostic
techniques” to rule out other causes of death (such as Castro-White’s asthma or steroid use).
Davis’s argument contains both legal and factual problems. Legally, we do not typically find
plain error where no “binding case law . . . answers the question presented[.]” United States v.
Al-Maliki, 787 F.3d 784, 794 (6th Cir. 2015) (citation omitted). And we have found no case
 No. 19-3094                           United States v. Davis                               Page 13


from our court (or others) holding that an autopsy is always a required “diagnostic technique”
before an expert may opine on a cause of death.

       Factually, Dr. Evans explained that coroners do not always need autopsies. If he can
identify the cause of death using other tools, he does so: “We don’t disturb a body if we don’t
need to disturb a body.” As far as we can tell on this record, Evans applied “the same level of
intellectual rigor that characterizes the practice of an expert in the relevant field.” Best, 563 F.3d
at 181 (citation omitted).

       Evans also explained why “an autopsy was not indicated” in this case, including the clear
signs of an overdose, as well as the fact that Castro-White was young and healthy. Although
Evans knew that Castro-White used steroids and had asthma, he did not need an autopsy to rule
out those factors. A steroid death would be “something completely different than what we saw.”
Steroids lead to “long-term problems but not usually acute problems like this.” Similarly, the
scene did not indicate that Castro-White had died of an asthma attack. A person having an
asthma attack experiences “air hunger” and will “go crazy trying to get air[.]” The person does
not “die[] laying in bed calmly.” A “foam cone” also does not usually occur outside narcotics
overdoses.

       None of Davis’s cases suggest the contrary. In Johnson v. Memphis Light Gas & Water
Division, 695 F. App’x 131 (6th Cir. 2017), for example, we noted that an expert’s “autopsy
report and testimony . . . demonstrate[d] that he sufficiently ruled out alternative causes of
death.” Id. at 141 (emphasis added). Johnson says nothing about whether an autopsy is always
necessary.

       Davis thus turns to the facts, attacking Dr. Evans’s reasons for dismissing asthma as a
cause of death.     Evans relied on a statement from Castro-White’s mother that he only
occasionally used an inhaler, but a friend testified that Castro-White had been using his inhaler
more often before his death. Davis also questions the basis for Evans’s belief that Castro-White
died calmly. Neither argument suggests that Evans’s approach was so unsound as to render his
opinion inadmissible. Although the lack of an autopsy may have affected the weight the jury
 No. 19-3094                           United States v. Davis                           Page 14


should give Evans’s opinion, it did not bar the opinion’s “threshold admissibility” on our plain-
error review. Best, 563 F.3d at 182.

                                         C. Jury Question

       Davis also challenges the district court’s response to a jury question about the phrase “on
or about.” The indictment charged Davis with distributing fentanyl “[o]n or about” March 7,
2016. Yet the parties’ evidence and argument showed that the distribution occurred specifically
on March 7. So Davis asked the district court to omit the pattern jury instruction defining “on or
about” to mean a date reasonably close in time to the date in the indictment. Davis did not want
the jury to think it could rely on other drug sales, especially because background evidence
showed that Davis had sold other drugs to Stock (who shared them with Castro-White) earlier on
March 6. The court agreed and omitted this instruction. Yet the parties’ proposed instructions
still used this undefined “on or about” phrase. They charged that “the Government must prove
that [Castro-White] died as a consequence of his use of the drugs[] that [Davis] distributed on or
about” March 7.

       During deliberations, the jury submitted the following question: “Charge 1 alleges that
Red distributed drugs ‘on or about March 7th.’ What is the time frame of ‘on or about?’” Davis
asked the court to respond “that the evidence presented was that the transaction involved
occurred on March 7 at 12:34 a.m.” The court responded differently: “‘On or about’ must be
viewed and framed in light of all the evidence the jury must reasonably consider in reaching a
verdict on Count 1 and, if applicable, the death enhancement.” Davis moved for a mistrial and a
new trial based on this response. The court denied his motions. It believed that the safest course
was to “refocus[] the jury on the evidence.” And since “[b]oth parties argued that the fatal
transaction occurred” on March 7, it was “pure speculation” to conclude that the jury would find
that other sales caused Castro-White’s death.

       On appeal, Davis argues that this supplemental instruction was legally wrong and
harmful because it allowed the jury to find that the drugs that Davis had sold earlier on March 6
caused Castro-White’s death. We see no prejudicial error.
 No. 19-3094                          United States v. Davis                              Page 15


       A district court responding to a question from a deliberating jury faces a difficult task.
The court “may and should make clear the law the jury is bound to apply[.]” United States v.
Rowan, 518 F.2d 685, 693 (6th Cir. 1975). Yet the court “must be careful not to invade the
jury’s province as fact-finder.” United States v. Nunez, 889 F.2d 1564, 1569 (6th Cir. 1989).
The court also must decide how best to resolve these competing concerns quickly to respect the
jury’s time. We thus typically leave the proper response to the district court’s “sound discretion”
and will reverse only if the court abuses that discretion in a way that causes prejudice. Id. at
1568 (citation omitted); see United States v. Castle, 625 F. App’x 279, 283 (6th Cir. 2015).

       When discussing the proper response to jury questions, our cases have drawn a
distinction between questions of law and questions of fact. If the jury asks a question about the
law, we have noted that the district court generally “should clear away its difficulties ‘with
concrete accuracy.’” Nunez, 889 F.2d at 1568 (citation omitted); United States v. Fisher, 648
F.3d 442, 448 (6th Cir. 2011). If the jury asks a question about the facts, we have noted that the
court may generally instruct the jury “to rely on its own recollection” of the evidence so as not to
bias its decisionmaking. United States v. McClendon, 362 F. App’x 475, 483 (6th Cir. 2010).

       Under this framework, the district court did not abuse its discretion. To begin with,
Davis put the court in a dilemma by advocating for the court to omit the definition of “on or
about” but ignoring that the parties’ proposed instructions used that phrase. The jury asked a
legal question about the meaning of the phrase “on or about.” To answer that question “with
concrete accuracy,” the court would have needed to give the very model instruction about “on or
about” that Davis opposed. Nunez, 889 F.2d at 1568 (citation omitted). Davis, by contrast,
asked the court to give a factual response to this legal question: “that the evidence presented was
that the transaction involved occurred on March 7 at 12:34 a.m.” This response would have
“invade[d] the jury’s province as fact-finder” by telling it what facts to find. Id. at 1569. Given
the circumstances, the district court did not abuse its discretion with what was essentially a
compromise ruling directing the jury to the evidence.

       Regardless, its response could not have caused “prejudice.”           Id. at 1568 (citation
omitted); United States v. Washington, 702 F.3d 886, 895 (6th Cir. 2012). We see no risk that
the jury based its verdict on the earlier March 6 sale because both parties presented a case that
 No. 19-3094                         United States v. Davis                              Page 16


Castro-White obtained the lethal drugs after midnight on March 7. So, when arguing for a
mistrial, Davis’s counsel agreed that “there’s literally zero evidence in the record that anything
that Castro-White obtained at 1:10 p.m. on March 6 was ingested by him which resulted in his
death.” And Davis asked to omit the “on or about” instruction precisely because the parties
offered no such theory. See United States v. Combs, 33 F.3d 667, 670 (6th Cir. 1994).

                                       D. Search Warrant

       Davis lastly challenges the district court’s denial of his motion to suppress evidence
seized from Davis’s home on the ground that the search violated his Fourth Amendment rights.

                                                1

       About a month after Castro-White’s death, Detective Sivert sought the warrant to search
Davis’s home. At trial, Sivert detailed his investigation during that month. Castro-White’s
iPhone was locked, but Sivert could see the missed calls from “Harry.”           He immediately
interviewed Karaplis. Karaplis lied to him by saying that he refused to help Castro-White buy
drugs. Karaplis also mentioned a person nicknamed “Red” as the possible drug source.

       Two days later, Sivert received Castro-White’s phone records from Verizon. On viewing
Castro-White’s texts with Karaplis and Stock, Sivert concluded that Karaplis had not been
“completely forthcoming.” In another interview, Karaplis told Sivert that Red was “some guy
from Lorain,” but denied having his phone number. He also told Sivert that the “Corey” in the
texts was Stock. When Sivert confronted Karaplis with the texts, Karaplis asked for a lawyer.
Sivert then talked to Stock. Stock said he bought drugs from Red at a Garden Avenue home.

       On April 1, Sivert interviewed Karaplis with a lawyer. Karaplis admitted his role. He
described Red and Red’s car and provided his phone number. Karaplis also pinpointed on
Google Maps the precise Garden Avenue home where he bought drugs from Red on March 7.
Sivert drove there. He spotted the car fitting the description that Karaplis had provided and ran
the license plate. The car belonged to “Russell Davis.” Additional research showed that Davis
went by the name “Big Red.”         Sivert also created a “photo array” of individuals with
characteristics like Davis’s, and Karaplis identified Davis with “100 percent” confidence.
 No. 19-3094                          United States v. Davis                           Page 17


       On April 11, Karaplis contacted Sivert about a text he received from Davis. At Sivert’s
request, Karaplis made a “controlled call” to Davis. When Karaplis referenced Castro-White’s
death, Davis asked: “How’d that turn out, did they sweat you a lot?” Sivert took Davis to be
asking whether the police had interrogated Karaplis about the fatal overdose.

       After this call, Sivert sought the warrant to search Davis’s home for his cellphone. His
affidavit to a magistrate at the Lorain County Municipal Court stated:

       1. In the early morning hours of . . . March 7, 2016, Jacob Castro-White was in
          contact with Zaharias Karaplis, another heroin user, for the purpose of
          obtaining heroin.
       2. Zaharias Karaplis and Jacob Castro-White made contact with a male known as
          “Red” and later identified as Russell Davis, on his cellular phone (216) 526-
          8810 for the purpose of purchasing heroin, both through text and voice
          communication.
       3. Zaharias Karaplis and Jacob Castro-White met with Russell “Red” Davis on
          March 7, 2016 for the purpose of buying heroin from him.
       4. Jacob Castro-White ingested the purported heroin from Russell “Red” Davis
          and it caused him to overdose. The time between the purchase of the heroin
          from Russell “Red” Davis and the estimated time of death, by the Lorain
          County Coroner Steven Evans is approximately one (1) hour.
       5. Toxicology tests conducted by the Lorain County Coroner’s Office revealed
          that Jacob Castro-White had a lethal dose of Fentynal in his sytem [sic].
       6. On April 12, 2016 at 0945 hours Zaharias Karaplis received a text message
          from Russell “Red” Davis via his cellular telephone with the number (216)
          526-8810.

The affidavit concluded that Sivert had “determined that Russell ‘Red’ Davis is trafficking in
heroin from the residence at 1832 Garden Avenue and is using his cellular telephone (216) 526-
8810 as an instrument of his trafficking business.”

       On April 12, the magistrate issued a warrant that authorized the police to search this
Garden Avenue address for a phone with the identified number, records “showing ownership” of
that phone, and records “that would identify those using/occupying” the residence. Police seized
Davis’s phone, paperwork, marijuana and cocaine, and drug-related accessories.
 No. 19-3094                           United States v. Davis                              Page 18


       Davis moved to suppress this evidence. He argued that the affidavit failed to show
probable cause that he lived at 1832 Garden Avenue and requested a hearing to decide whether
Sivert deliberately omitted Karaplis’s initial lies. See Franks v. Delaware, 438 U.S. 154 (1978).
The government’s response identified the steps Sivert took to connect Davis to this home.
Although the affidavit omitted this information, the government believed that the magistrate
would “testify that when appropriate he takes additional information from each affiant before
issuing a warrant, which he then considers in unison with the affidavit[.]” And it expected to
show that Sivert and the magistrate discussed the case before the magistrate issued the warrant.

       The district court scheduled a hearing, but later denied the motion without one. It held
that the affidavit established a nexus between “the alleged criminal activity and [Davis’s]
residence.” Relying on the government’s brief (not evidence), the court noted that Karaplis
identified Davis’s home as the place of the drug buy and concluded that this identification
established probable cause that Davis’s phone would be found there.

                                                  2

       Davis asserts three claims on appeal: that the magistrate lacked the authority to issue the
warrant; that the warrant lacked probable cause linking Davis to the place to be searched; and
that we should order a “Franks hearing” over whether the affidavit omitted material information.
We reject Davis’s first claim on plain-error review. And we accept the government’s request for
a limited remand on his second claim, so we need not consider Davis’s request for a hearing.

       a. Magistrate’s Authority. Davis asserts that the warrant violated the Fourth Amendment
because the magistrate lacked the authority to issue it under Ohio law. Yet Davis never raised
this claim in the district court, so we review it only for plain error. See United States v.
Ramamoorthy, 949 F.3d 955, 962 (6th Cir. 2020). Davis’s short analysis on this issue may
(or may not) have identified an “error,” but it is certainly not one that we would call “plain.”

       The Fourth Amendment says that warrants “shall issue” only in certain circumstances,
but does not identify who may issue them. The Supreme Court has set two rules: The issuer
“must be neutral and detached, and he must be capable of determining whether probable cause
exists for the requested arrest or search.” Shadwick v. City of Tampa, 407 U.S. 345, 350 (1972).
 No. 19-3094                           United States v. Davis                              Page 19


Beyond this floor, states have “flexibility to determine who has the authority to issue warrants[.]”
United States v. Master, 614 F.3d 236, 240 (6th Cir. 2010). And if a search otherwise complies
with the Fourth Amendment, the Court generally holds that it does not matter that the search
violated some state requirement. Virginia v. Moore, 553 U.S. 164, 176 (2008). Yet we have
carved out an exception to that rule in this context: “State law determines what person is allowed
to approve what warrant,” so a warrant issued by a person lacking state-law authority violates the
Fourth Amendment too. Master, 614 F.3d at 239–41; United States v. Scott, 260 F.3d 512, 515
(6th Cir. 2010); cf. United States v. Krueger, 809 F.3d 1109, 1123–24 (10th Cir. 2015) (Gorsuch,
J., concurring).

       Here, a “magistrate” of the Lorain County Municipal Court issued the warrant. See Ohio
Crim. R. 19. Whether this magistrate could validly do so raises a difficult state-law question.
The Ohio statutes and rules governing the question are somewhat circular, the Ohio Supreme
Court has not resolved the question, and few courts have considered it. On the one hand, state
law provides that, after receiving a sufficient affidavit, “the judge or magistrate . . . shall issue
the warrant, identifying in it the property and naming or describing the person or place to be
searched.” Ohio Rev. Code § 2933.23. It thus permits two categories of officials to issue
warrants: judges and magistrates. On the other hand, this law defines magistrate to “include[]
county court judges, police justices, mayors of municipal corporation, and judges of other courts
inferior to the court of common pleas.” Id. § 2931.01(A). It does not expressly include court-
appointed “magistrates” under Ohio Rule of Criminal Procedure 19. And Ohio Rule of Criminal
Procedure 2(F) defines “magistrate” for purposes of those rules not to “include an official
included within the definition of magistrate contained in” the law. Ohio Crim. R. 2(F). That fact
has led some state courts to hold that court-appointed magistrates may not issue warrants. State
v. Kithcart, 995 N.E.2d 918, 923–24 (Ohio Ct. App. 2013); State v. Commins, 2009 WL
4574886, at *4 (Ohio Ct. App. Dec. 7, 2009).

       The magistrate in this case thus may well have lacked authority to issue the warrant. But
we need not resolve this point because no error was “obvious.” See Ramamoorthy, 949 F.3d at
960. We “cannot correct an error pursuant to Rule 52(b) unless the error is clear under current
law.” United States v. Olano, 507 U.S. 725, 734 (1993). The alleged state-law error here does
 No. 19-3094                           United States v. Davis                           Page 20


not meet this test, at least not when viewed from the perspective of a federal court. To the
contrary, the state law on this legal issue is both unclear and “undeveloped.” United States v.
Christensen, 828 F.3d 763, 790 (9th Cir. 2015); United States v. Bain, 874 F.3d 1, 30–31 (1st
Cir. 2017).

          b. Probable Cause. Davis also argues that Sivert’s affidavit did not establish probable
cause to search 1832 Garden Avenue because it included no facts connecting Davis to this home.
For an affidavit to establish probable cause, our precedent requires the affidavit to contain a
sufficient nexus between the evidence sought and the place to be searched. United States v.
Hang Le-Thy Tran, 433 F.3d 472, 482 (6th Cir. 2006); United States v. Carpenter, 360 F.3d 591,
594 (6th Cir. 2004) (en banc). The government now concedes that Sivert’s affidavit did not
contain enough facts tying Davis (and his phone) to this location. It raises two other arguments.
The government asserts that if the admission of evidence seized from Davis’s home violated the
exclusionary rule, the error was harmless in light of the other evidence showing his guilt.
Alternatively, it argues that we should issue a limited remand for a hearing because Sivert gave
additional oral testimony to the magistrate. We opt for the second course without resolving the
first. The hearing could obviate the need to conduct this harmlessness inquiry. And the district
court, having overseen the trial, should initially conduct the inquiry if it turns out to be
necessary.

          The Fourth Amendment provides that “no Warrants shall issue, but upon probable cause,
supported by Oath or affirmation[.]” U.S. Const. amend. IV. This “text does not require oral
testimony to be transcribed or otherwise recorded. Nor did the American legal tradition at the
time of the Fourth Amendment’s adoption.” United States v. Patton, 962 F.3d 972, 974 (7th Cir.
2020) (citing William J. Cuddihy, The Fourth Amendment: Origins and Original Meaning 602–
1791, at 754–58 (2009)). We thus have long held that an affiant may supplement an inadequate
affidavit with factual allegations “presented to the magistrate through sworn oral testimony.”
Hang Le-Thy Tran, 433 F.3d at 482 (citing United States v. Shields, 978 F.2d 943, 946 (6th Cir.
1992)).

          The government asserts that this process occurred here: The magistrate “recognized that
[the warrant] was deficient and took additional oral information” before issuing it. Arg. 23:10–
 No. 19-3094                          United States v. Davis                             Page 21


28. Detective Sivert’s trial testimony, moreover, showed that he undertook significant efforts to
connect Davis to the residence at 1832 Garden Avenue before seeking the warrant. He had
learned that Davis lived at this location through interviews with Karaplis and Stock and had
driven to the location and viewed a car registered to Davis parked there. As the district court
noted, this evidence would establish the required nexus between Davis and the location. See
Hang Le-Thy Tran, 433 F.3d at 482; cf. United States v. Feagan, 472 F. App’x 382, 394 (6th Cir.
2012); United States v. Williams, 544 F.3d 683, 688 (6th Cir. 2008). Yet the district court relied
on statements in the government’s brief for these facts, not statements in evidence. No evidence
tells us whether Sivert conveyed these facts under oath to the magistrate before the magistrate
issued the warrant, as the government claims. Cf. Patton, 962 F.3d at 973–74. The government
had planned to introduce evidence detailing this testimony, but the district court opted to resolve
the motion without a hearing. So we lack factual findings from the district court on what Sivert
told the magistrate.

       As we have done in similar circumstances, we will order a remand “for the limited
purpose” of conducting an evidentiary hearing on this probable-cause question. See United
States v. Beals, 698 F.3d 248, 268 (6th Cir. 2012); 28 U.S.C. § 2106. Either party may then
appeal, as appropriate, from the district court’s resolution. Beals, 698 F.3d at 268; 18 U.S.C.
§ 3731; 28 U.S.C. § 1291.

                                             * * *

       We reject most of Davis’s claims on the merits. But we issue a limited remand for
further proceedings consistent with this opinion on his Fourth Amendment claim.
