In the 

United States Court of Appeals 

For the Seventh Circuit ____________________

No. 18‐1002

UNITED STATES OF AMERICA,

Plaintiff‐Appellee,

v.

JABOREE WILLIAMS,

Defendant‐Appellant.

____________________

Appeal from the United States District Court for the

Eastern District of Wisconsin.

No. 2:16‐cr‐00111‐JPS‐1 — J. P. Stadtmueller, Judge.

____________________

ARGUED MAY 24, 2018 — DECIDED AUGUST 15, 2018

____________________

Before MANION and BARRETT, Circuit Judges, and

GETTLEMAN, District Judge.*

BARRETT, Circuit Judge. Jaboree Williams argues that his

conviction was tainted by improperly admitted expert testi‐

mony. He maintains that the government violated the expert

disclosure rules by giving him inadequate notice of what its

                                                 

* Of the Northern District of Illinois, sitting by designation.
2 No. 18‐1002

expert planned to say at trial. Moreover, he says that the gov‐

ernment used the expert’s testimony to make an argument

that the Federal Rules of Evidence prohibit: that he had the

character of a sex trafficker and was therefore likely to have

committed sex‐trafficking crimes.

While the government did not violate the rules prohibiting

the use of character evidence, it probably did violate the ex‐

pert disclosure requirement. Nonetheless, we affirm Wil‐

liams’ conviction because any error was harmless. The evi‐

dence of his guilt was so overwhelming that the jury would

surely have convicted him even if the government’s expert

had not testified.

I.

Jaboree Williams was accused of myriad offenses relating

primarily to a wide‐ranging sex‐trafficking scheme. We won’t

recount every sordid detail of Williams’ scheme; suffice it to

say that he lured women in desperate circumstances into

prostitution by convincing them that he would take care of

them. He then maintained control over these women through

brutal physical abuse. He was indicted on numerous charges

relating to sex trafficking, prostitution, heroin, obstruction of

justice, and extortion.

Before trial, the government filed a notice of its intent to

call Amy Mentzel, an FBI agent, as an expert witness. The no‐

tice adequately described Mentzel’s credentials and her career

with the FBI. But its summary of her anticipated testimony

was sparse: it listed a series of broad topics without any ex‐

planation of what she would say about each. For example, it

stated that she would testify about “the recruiting processes
No. 18‐1002 3

used by pimps,” “the methods pimps and those they prosti‐

tute use to advertise their services and acquire customers,”

and “other aspects of human sex trade involving adults and

juveniles.” It offered no detail about what Mentzel would say

about recruiting, advertising, or any other aspect of the sex

trade.  

Williams moved to exclude Mentzel from testifying on the

ground that the expert disclosure was inadequate and her tes‐

timony would not help the jury. The district court deferred

consideration of that motion, and when the government in‐

troduced Mentzel as a witness at trial, Williams renewed his

objections. He repeated his argument that the expert disclo‐

sure had been inadequate under Federal Rule of Criminal

Procedure 16(a)(1)(G), which requires that the disclosure con‐

tain “a written summary of any [expert] testimony that the

government intends to use” in its case‐in‐chief. And he again

insisted that Mentzel’s testimony would not help the jury—

the court’s jury instructions would define the crime of human

trafficking for the jurors, so he said that they would need no

additional guidance on that point. He also referred the district

court back to the motion he had originally filed to exclude

Mentzel on the ground that her testimony would be imper‐

missible character evidence.

The court overruled these objections, and Mentzel testi‐

fied. She told the jury about how a human trafficker preys on

vulnerable young women and makes them think that they’re

in a “boyfriend/girlfriend type of relationship” before having

them go on prostitution “dates.” She talked about how pimps

coerce their victims through fraud and force, how they handle

money, how they punish their victims to ensure obedience,

how they organize their operations, what certain terminology
4 No. 18‐1002

means (like “trick” and “incall”), and the sorts of rules they

set for their victims. Mentzel did not testify about Williams or

his actions, as she had not been involved in his case.

Mentzel’s expert testimony was a small part of a trial in

which the lay testimony was substantial. Three of Williams’

victims testified about how Williams recruited them to pros‐

titution, set up prostitution “dates” in numerous states, laid

down rules for those “dates,” controlled and kept any pay‐

ment, violently punished them for breaking any of his rules,

and threatened them to ensure obedience. One victim testified

that Williams knew about her addiction to Percocet and with‐

held the drug as a means of controlling her. There was also

testimony that Williams choked one victim to the point of un‐

consciousness, stomped on one in a bathtub, beat one with a

belt, punched one in the face, broke one victim’s nose, and

more. A woman named Heller, who was romantically linked

to Williams but did not engage in prostitution, testified that

Williams admitted to prostituting several of the testifying vic‐

tims. Heller often picked Williams and his victims up from

hotels where Williams had forced them to service his clients.

She also listened as Williams physically abused one of his vic‐

tims. Another witness, one of Williams’ longtime friends, told

the jury that Williams had both introduced one of the testify‐

ing victims as his prostitute and bragged about his pimping

activities.

The documentary evidence was similarly ample. There

were pictures of injuries that Williams had inflicted on his vic‐

tims. There were online prostitution ads for each of the testi‐

fying victims, all linked to Williams’ email addresses. There

were text messages and Facebook messages in which Wil‐

liams admitted that he was a pimp and referred to the same
No. 18‐1002 5

victims who later testified at his trial. In short, the evidence

against Williams was overwhelming.

The jury convicted Williams of almost all of the charged

crimes, and he now appeals that conviction.

II.

Williams argues that the court should have excluded

Mentzel’s testimony, because the government’s expert disclo‐

sure was insufficient. Federal Rule of Criminal Procedure

16(a)(1)(G) requires the government to provide a “written

summary” of the expert testimony it intends to introduce, and

the government cannot satisfy that obligation by merely

providing a “list of topics.” United States v. Duvall, 272 F.3d

825, 828–29 (7th Cir. 2001). To help the defendant prepare for

trial, the disclosure must summarize what the expert will ac‐

tually say about those topics. Id. The government’s disclosure

of Mentzel’s testimony was plainly inadequate under that

standard, because it did no more than list a series of topics

that she planned to cover.  

The government, however, argues that this standard does

not apply. According to the government, a written summary

must include more than a list of topics only when an expert

provides opinion testimony. And Mentzel did not provide

opinion testimony; she provided “background, educational

testimony.” Thus, the government says, the list it provided

was enough to satisfy Rule 16(a)(1)(G).

There are serious reasons to doubt the government’s posi‐

tion. The “written summary” requirement of Rule 16(a)(1)(G)

applies to “any testimony that the government intends to use

under Rule[] 702,” and Rule 702 governs both experts who of‐

fer an opinion and those who don’t. And in defining the
6 No. 18‐1002

phrase “written summary,” we have stated broadly and une‐

quivocally that Rule 16(a)(1)(G) “requires a summary of the

expected testimony, not a list of topics.” Duvall, 272 F.3d at

828. Neither the rule nor our interpretation of it suggests that

“written summary” means something different for non‐opin‐

ion experts.  

That said, any deficiency in the written summary was

harmless. As an initial matter, Williams has not shown that

the lack of detail affected his ability to present a defense. For

example, he has not shown that he was “unduly surprised”

by Mentzel’s testimony. United States v. Thornton, 642 F.3d 599,

606 (7th Cir. 2011) (holding that a defendant was not preju‐

diced by an inadequate Rule 16 disclosure where he “ha[d]

not demonstrated, for example, that he was unduly surprised

or lacked an adequate opportunity to prepare a defense”). His

opening brief does say in passing that the vague notice made

it impossible for him to evaluate whether he needed an expert

witness of his own to rebut Mentzel’s testimony. But he does

not assert, let alone show, that he actually would have consid‐

ered having his own expert testify had the notice been more

detailed. He also argues that the sparse notice made it difficult

for him to make, and for the district court to assess, other ar‐

guments against the admission of the testimony. Yet his sub‐

stantive objection to the testimony is meritless—we will say

more about that below—so any impediment to making that

objection was harmless.

Moreover, any error in admitting Mentzel’s testimony

“could not have made any difference” to the outcome. Duvall,

272 F.3d at 829. To evaluate whether an error was harmless,

we consider “whether the prosecution’s case would have

been significantly less persuasive in the mind of the average
No. 18‐1002 7

juror if the erroneously admitted evidence had been ex‐

cluded.” United States v. Saunders, 826 F.3d 363, 370 (7th Cir.

2016). Williams has conceded that the testimony of his victims

was more than adequate to convince the jury that he was

guilty of the charges for which he was convicted, and “[t]he

question for the trial was whether the women should be be‐

lieved.” Nothing in Mentzel’s testimony bore on whether the

women who testified should be believed, and we see no rea‐

son that an average juror would find the prosecution’s case

less compelling without Mentzel’s description of how sex traf‐

ficking works.

III.

Williams objects to Mentzel’s testimony for another rea‐

son: he says that it should have been excluded as evidence of

a “group character trait.” The prosecution ordinarily cannot

introduce “[e]vidence of a person’s character or character

trait ... to prove that on a particular occasion the person acted

in accordance with the character trait.” Fed. R. Evid. 404(a)(1).

Williams argues that the government used Mentzel’s testi‐

mony to show that he had the character of a typical sex traf‐

ficker and was therefore likely to have engaged in sex traffick‐

ing.

This argument fails, because Mentzel’s testimony was not

designed to illustrate the “character” of a typical sex traf‐

ficker. Although it is difficult to give a comprehensive defini‐

tion of “character evidence,” we generally interpret it as “ev‐

idence that ‘refers to elements of one’s disposition, such as

honesty, temperance, or peacefulness,’ which shows a pro‐

pensity to act a certain way in a certain situation.” United

States v. Romero, 189 F.3d 576, 587 (7th Cir. 1999) (quoting

United States v. Doe, 149 F.3d 634, 638 (7th Cir. 1998)). Rule 404
8 No. 18‐1002

prohibits “an attempt to use a person’s personality or psycho‐

logical propensity to prove what the person did.” Id.

Because of this rule, Mentzel could not have testified about

the character of sex traffickers to raise the forbidden inference

that Williams’ similar character made him likely to engage in

sex trafficking. For example, she could not have testified that

sex traffickers are violent people likely to brutalize women so

that the government could then argue that Williams was also

violent and thus likely to brutalize women. Nor could the

government have used Mentzel’s testimony to make the same

point indirectly by relying on the acts of both sex traffickers

and Williams to raise the forbidden inference about how peo‐

ple with a certain character trait are likely to behave. Rule

404(b)(1) (“Evidence of a crime, wrong, or other act is not ad‐

missible to prove a person’s character in order to show that

on a particular occasion the person acted in accordance with

the character.”) For example, the government could not have

used Mentzel’s testimony about what sex traffickers do as

proof that they are violent people likely to act in accordance

with that violent character, and that Williams’ behavior

shows that he too is violent and therefore also likely to act in

accordance with that violent character.

But that is not what the government did. Mentzel’s testi‐

mony was not about the propensity of people with a certain

disposition to commit sex‐trafficking crimes. Nor did the gov‐

ernment use Mentzel’s testimony to illustrate that the acts of

sex traffickers revealed that they had a certain disposition that

made them likely to commit sex‐trafficking crimes. Nor did

the government use that evidence to argue that Williams had

the disposition of a sex trafficker and was therefore likely to

have committed sex‐trafficking crimes. The government used
No. 18‐1002 9

Mentzel’s testimony about the acts of sex traffickers to illus‐

trate their modus operandi, not their character; it suggested

that because Williams employed similar techniques, his be‐

havior was evidence that he too was engaged in a sex‐traffick‐

ing operation. Rule 404’s prohibition on character evidence is

inapplicable, because there were no arguments about charac‐

ter at play.

We have repeatedly rejected essentially the same argu‐

ment that Williams makes now. For example, in United States

v. Romero, the defendant was a pedophile accused of using the

internet to lure underage boys away from their homes, and

the government introduced an expert witness who discussed

the actions of sex offenders to “explain their techniques or

modus operandi.” 189 F.3d at 587. We rejected the defendant’s

argument that the expert’s testimony was impermissible char‐

acter evidence under Rule 404. The government did not use

that testimony to argue that the defendant’s poor character

made him likely to sexually abuse children. It used that testi‐

mony to show that his actions were consistent with common

tactics that pedophiles used to lure their victims. Id.  

United States v. Doe is another example. 149 F.3d 634 (7th

Cir. 1998). There, the defendant was accused of being part of

a Nigerian smuggling operation that trafficked heroin from

Southeast Asia to the United States. Id. at 636. The govern‐

ment introduced an expert witness who testified about the

practices of such Nigerian drug‐smuggling operations and

how they get their drugs into the country. Id. We held that this

testimony was not impermissible group character evidence,

because it did not “suggest[] that [the defendant] had a ‘pro‐

pensity’ to import or distribute drugs.” It “served only to illu‐

minate the modus operandi of Nigerian importers of Southeast
10 No. 18‐1002

Asian heroin” so that the jury would have useful context “in

evaluating proposed explanations of [the defendant’s] ob‐

served behaviors.” Id. at 638.  

The same is true here. The government did not introduce

Mentzel’s testimony to show that Williams’ flawed character

predisposed him to human trafficking. Instead, the point of

the evidence was to show that Williams’ actions were con‐

sistent with the management of a sex‐trafficking scheme.  

* * *  

Any deficiency in the government’s notice was harmless,

and Mentzel’s expert evidence was not inadmissible character

evidence. The district court’s judgment is AFFIRMED.