The law seeks the truth; science seeks the facts. The two frequently clash in a court of law.


The Texas Rules of Evidence permit two kinds of opinion testimony—lay and expert. Rule 701 permits the lay testimony of the more traditional witness, like those who either saw or participated in the events surrounding the crime charged. Rule 702 permits the specialized testimony of an “expert” witness.


Lay opinion testimony encompasses both a witness’s perceptions and experiences associated with the event about which they are testifying, including what they saw, heard, smelled, touched, felt, or tasted. Expert opinion testimony, however, is dependent upon “the degree of education, training, or experience a witness should have before he can qualify as an expert is directly related to the complexity of the field about which he proposes to testify.” The admission of the latter testimony is predicated on three basic factors:


  1. The witness must be qualified in the area of expertise for which the evidence is proffered;
  2. The expert’s testimony must be grounded in the scientific, technical, or other specialized knowledge in that particular area of expertise; and
  3. The testimony must assist the trier of fact.


While the Texas Court of Criminal Appeals has never addressed the issue of whether a witness with training and experience can testify as a lay witness, the court has authorized the admission of such testimony as both lay and expert opinion. In other words, a witness with specialized knowledge may testify about their own observations under Rule 701 and testify about the theories, facts and data used in their own area of expertise under Rule 702.


Texas prosecutors often use law enforcement officers to give both lay and expert testimony, resulting in nasty head-butting between truth and science. The experiences and observations gleaned by law enforcement during the investigation and apprehension process are too frequently presented as specialized knowledge. For example, the courts have recognized law enforcement opinion testimony under both Rule 701 and 702 in the following situations:


  • Ventroy v. State – police officer’s experience and personal knowledge about the scene of an accident;
  • Yohey v. State – police officer’s testimony regarding time of death;
  • Austin v. State – police officer’s testimony that “Swedish Deep Muscle Rub” was a term for prostitution;
  • Reece v. State – police officer’s testimony that, in his opinion, based on experience, the actions he observed were consistent with someone selling drugs;
  • State v. Wilson – police officer’s testimony as non-expert opinion witness regarding intoxication based in part on smelling the odor of alcohol.


The following are examples of law enforcement testifying purely as “expert” witnesses under Rule 702:


  • Thompson v. State – police officer with only 40 hours of training to interpret phone records permitted to testify as expert when the technique used was not complex;
  • Perryman v. State – police officer permitted to testify about profile of sexual assault victim’s assailant;
  • Thomas v. State – police officer allowed to testify as expert regarding the procedures of a con game known as a “pigeon drop” scheme; and
  • Sabedra v. State – police officer permitted to testify as expert regarding his knowledge about stab wounds and to opine about whether the victim’s wounds were serious and permanent.


In each of these “expert” cases the courts made a finding that specialized opinions by the law enforcement officers were either helpful to or in some way aided the jury in its effort to determine the truth.


In his 2008 Catholic University Law Review article, “Acts of Emotion: Analyzing Congressional Involvement in the Federal Rules of Evidence,” Georgetown University Law Center Teaching Fellow Michael Teter observed that allowing law enforcement officers to testify as “experts” was a “dramatic unintended” consequence of Federal Rule 702.


We agree.


Law enforcement officers testifying as “experts” about gang involvement, drug profiling, and other areas beyond the bounds of the knowledge they gain through work experience corrupts the truth seeking process.  Law enforcement testimony in the courtroom has turned perception into reality, opinion into fact.


We acknowledge there is some evidence that requires both lay and expert testimony to clarify some evidence for the jury.  Law enforcement testimony, however, is not one of them. Law enforcement experience, even expertise, belongs in the investigation and apprehension process, and it should remain there. The truth is simply this: there should be no creature called “expert” law enforcement testimony. The testimony of police officers should be nothing more than a presentation of factual observations and facts. Juries should not be influenced by the “junk science” of expert law enforcement testimony.