661.1Crime and Criminal Practices

Last Updated: 12/01/23

Key Concepts

  • A properly qualified expert may be permitted to testify as an expert regarding various criminal practices, such as the use of gang signs and terminology, or the methods and strategies commonly employed by drug traffickers.
  • The admissibility of criminal practices opinion testimony has not yet been reconsidered by North Carolina’s appellate courts applying the Daubert standard, but federal courts examining this issue have generally allowed it.
  • When a witness offers “dual testimony,” testifying as both a fact witness and an expert in the same trial, the two lines of inquiry must be kept separate or it may be viewed as error on appeal.


North Carolina trial courts have consistently allowed properly qualified witnesses, including law enforcement officers who are qualified based on their years of training and experience, to testify about “criminal practices” (that is, the common or preferred methods, tactics, slang, habits, etc. of criminals) in a wide variety of areas. See, e.g., State v. Jennings, 209 N.C. App. 329 (2011) (police sergeant permitted to testify as an expert regarding various methods that criminals use to conceal evidence of illegal conduct committed on their computers); State v. Brockett, 185 N.C. App. 18 (2007) (though not formally tendered as an expert, detective was implicitly received as one and permitted to testify about the meaning of gang terminology the defendant used in a recorded phone call); State v. Alderson, 173 N.C. App. 344 (2005) (holding trial court properly permitted SBI agent to “give her opinion as to why the seizure of defendant's police frequency book was important, testifying that finding a police frequency book and a radio scanner can indicate those acting illegally may have a ‘jumpstart’ if they know which police frequencies to monitor”); State v. White, 154 N.C. App. 598 (2002) (officer was qualified by training and experience to give an opinion that the presence “of an object such as a pillow or a cloth being placed over somebody's face can mean in a case that the perpetrator knew the victim and did not want to see their face or have their face appear either before, during, or after the crime,” and finding that this testimony was likely to assist the jury in making an inference from the circumstances of the crime); State v. Moore, 152 N.C. App. 156 (2002) (“the length of Dennis’s employment as a narcotics officer, as well as his knowledge of cocaine manufacturing, the division and packaging of the drug, and his extensive knowledge of illegal drug operations, all provided him with the requisite expertise to testify to a hypothetical question” about whether the facts of this case indicated a drug operation, and this opinion “was helpful to the trier of fact and did not invade the province of the jury”); see also State v. Johnson, 219 N.C. App. 651 (2012) (issue was not properly preserved for review on appeal, but noting that trial court allowed officer to testify as a gang expert regarding the use of slang terms and the process of gaining “status” within a gang by committing criminal “missions”).

Practice Pointer

Expert witness on criminal law?
The discussion above addresses expert testimony about criminal practices and conduct – but what about calling an expert witness to testify about criminal law itself? For example, could a law professor be called to testify as an expert on statutory interpretation, or an appellate judge to offer an opinion on the level of proof needed for particular elements such as intent or the use of deadly force? Although that type of testimony might be admissible in certain proceedings (e.g., for an MAR claiming ineffective assistance of counsel), at a routine criminal trial such testimony would likely be viewed as improperly invading the province of the jury. For a more detailed discussion and a summary of some relevant cases on this issue, see Legal Expert Witnesses,” Jeff Welty, North Carolina Criminal Law Blog, May 23, 2012.

Admissibility and Reliability

Daubert and Rule 702

The cases cited above were all decided before the 2011 amendment to Rule 702 that made North Carolina a Daubert state. There are not yet any North Carolina appellate cases analyzing the admissibility of this type of expert testimony under the Daubert standard. However, federal courts applying the same standard have consistently allowed such testimony, as long as the witness is properly qualified and the testimony is relevant and helpful to the jury. See, e.g., United States v. Palacios, 677 F.3d 234 (4th Cir. 2012) (no abuse of discretion in allowing qualified officer to give “expert testimony on the gang’s development, organization, policies, practices, and symbols”); United States v Wilson, 484 F.3d 267 (4th Cir. 2007) (district court did not abuse its discretion in ruling that police detective was qualified to testify as expert on the translations of code words used by drug traffickers); United States v. Duarte, 581 Fed. Appx. 254 (4th Cir. 2014) (unpublished) (trial court allowed IRS agent to testify as an “expert in money laundering” – appellate court held it was not an abuse of discretion where “[t]he organization used a variety of methods to return the cash proceeds to Guatemala” and “the testimony would be helpful and [the witness’s] experience was sufficient to qualify him as an expert”); United States v. Lobo-Lopez, 468 Fed. Appx. 186 (4th Cir. 2012) (unpublished) (affirming trial court’s decision to allow detective to testify as an expert based on training and experience in gang investigations – witness’s testimony “‘shed light on’ the internal structure, rules, terminology, and methods of MS–13”); see also United States v. Garza, 566 F.3d 1194 (10th Cir. 2009) (““[W]e do not believe that Daubert and its progeny . . . provide any ground for us to depart from our pre-Daubert precedents recognizing that police officers can acquire specialized knowledge of criminal practices and thus the expertise to opine on such matters as the use of firearms in the drug trade.”); but see United States v. Norwood, 16 F. Supp. 3d 848 (E.D. Mich. 2014) (excluding proffered expert testimony concerning gangs where the witness formed his opinions based on his experience in Oklahoma, California, Connecticut, and Washington, D.C., but the case in question concerned a gang that operated in Michigan, and stating that “[s]imply put, [the witness’s] lack of familiarity with the particular gang or locale at issue in this case makes his opinions unreliable to be placed before the jury”).

Dangers of “Dual Testimony”

When a witness testifies as both a fact witness (providing details about the investigation that was conducted in this particular case) and as an expert witness on criminal practices (offering an opinion about the typical behaviors or practices associated with this type of crime in general), the party eliciting that testimony must ensure that the two lines of inquiry are kept separate; otherwise, there is a risk that the witness’s testimony will confuse the jury by blurring the distinction between fact and opinion. See U.S. v. Palacios, 677 F.3d 234 (4th Cir. 2012) (state’s witness testified as both an expert in gangs generally, and as one of the investigators in the case at issue: “The district court permitted Norris to testify in both capacities, but it required the government to indicate when it was transitioning from Norris's expert opinion to his personal observations.”). Some courts have also expressed a concern that the jury will give the factual testimony of that witness an undue “aura of special reliability,” due to the witness’s qualification as an expert. See U.S. v. York, 572 F.3d 415 (7th Cir. 2009).

If the state fails to clearly distinguish between the witness’s factual testimony about his or her personal observations and his or her opinion testimony based on the witness’s training and experience, the defendant could be unfairly prejudiced and the case may be reversed on appeal. See U.S. v. Garcia, 752 F.3d 382 (4th Cir. 2014) (conviction vacated where there were inadequate safeguards to protect jury in drug prosecution from conflating federal agent's testimony as both a decoding expert and a fact witness – agent moved back and forth between expert and fact testimony with no distinction in prosecutor's questioning or in agent's answers, and the record did not demonstrate whether agent's conclusions were based on her independent assessments of the words used or her after-the-fact debriefing of non-testifying co-conspirators).

Practice Pointer

Call two witnesses
Rather than inviting error and risking reversal on appeal by eliciting “dual testimony” from a witness, the prosecutor may want to call a separate witness to offer expert testimony about the criminal practices. For example, another experienced narcotics detective who was not involved in the investigation of this defendant’s drug trafficking case could be called to testify immediately after the state’s lead investigator testifies. The lead detective could testify about the baggies, twist ties, baking powder, and digital scales found on the defendant’s living room table, and the second detective could provide expert opinion testimony about the significance and usual purpose of those items.
If the use of a second, “expert-only” witness is not an option, the prosecutor needs to carefully plan his or her questions in advance to ensure that there is a bright line drawn between fact and opinion testimony. For example, the prosecutor could clearly signal the transition from expert opinion testimony into factual lay witness testimony by stating “officer, let’s now move into looking at the work you did as an investigator in this particular case….”

Portions of this entry were excerpted from the North Carolina Superior Court Judges’ Benchbook, “Criminal Evidence: Expert Testimony,” Aug. 2017, Jessica Smith