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Expert Witnesses for the Prosecution are Not Invincible

Posted on November 9, 2023 in
Arizona Criminal Law & Expert Witnesses

The state can use several types of evidence against a defendant in a criminal trial, including expert witnesses. Expert witnesses often have an air of invincibility. People who are charged with a crime and face an expert witness at trial may feel intimidated. Moreover, some jurors think, “Well, he is an expert; we cannot really doubt what he says.” A Phoenix defense attorney with knowledge and experience can often limit or even prevent damage from an expert witness’ testimony.

Expert witnesses are fallible humans who often have their own agenda. Moreover, they offer opinions, not facts.


Defense attorneys can limit the testimony of expert witnesses to those subjects in which they are experts. For example, a mechanic who specializes in repairing transmissions in Ford Mustangs could be offered as an expert witness on Mustang transmissions. However, his testimony on whether the braking system was deliberately damaged would be suspect and could be kept out as evidence.

District attorneys want to win. Consequently, they often try to impress the jury with an expert witness. The defense attorney needs to be on guard that the state does not try to interject the expert witness’s testimony into areas where he does not have any expertise.


When conducting forensic tests, the correct protocol must be in place, and the expert witness must follow the protocol. In Durham, North Carolina three lacrosse players from Duke University were charged with rape. As part of the prosecution’s case, testing was conducted to find semen or other evidence of rape on the alleged victim. Next, an expert witness conducted DNA testing on the specimen collected from the woman.

Tests revealed the DNA found on the woman did not come from any of the Duke lacrosse players. The results were reported to the district attorney. The district attorney encouraged the head of the lab to omit from his report that none of the semen came from the three defendants. The lab chief complied with the district attorney’s request and did not include the test results that indicated none of the semen came from the defendants.

The defense team uncovered the intentional violation of protocol by carefully reviewing the results of the DNA test. When questioned by a defense attorney, the head of the lab that conducted the test admitted he failed to follow proper protocol in preparing his reports.

In the end, North Carolina’s Attorney General intervened and the case against the lacrosse players was dismissed. The district attorney was disbarred for his misconduct. An article on misdeeds of the expert witness in Duke lacrosse rape case can be found at the following link. Duke Rape Case.

In the Duke rape case, the lab failed to follow proper protocol in preparing a report. However, the tests are also required to be conducted correctly. Therefore, a good defense attorney will check to see if tests were performed according to proper technical protocol.


Expert witnesses may not intentionally mislead a jury or judge, but their own biases can lead to faulty conclusions. In one case, a psychologist testified that a particular child exhibited behaviors that were consistent with those of a child who had been subjected to sexual abuse. However, no physical evidence of sexual abuse was found and the child denied being abused. The psychologist further testified that sexually abused children often deny that they have been sexually abused.

The psychologist had been practicing for several years. She was asked, of all the children she had examined, how many did she find who were not sexually abused. The psychologist could not recall a single child she examined that she did not believe was sexually abused, not one.

The psychologist worked closely with the district attorney’s office and a local center for abused children. Moreover, she stated any behavior could be consistent with a child who was sexually abused. One could conclude the psychologist was so horrified by the idea of sexually abused children she lost objectivity. Moreover, she was surrounded by professionals who also worked from the assumption every accusation of sexual abuse is true. An effective attorney can reduce the credibility of an expert witness like this by exposing the expert witness’s bias.

The Little Rascals Day Care sexual abuse case in Edenton, North Carolina also indicates how expert witnesses can draw wrong conclusions because of professional bias. The co-owners and workers at the center were charged with sexually abusing children. Children who attended the center denied sexual abuse occurred, but a therapist disregarded the denials. The owners and some of the workers were convicted at trial.  The convictions were overturned on appeal, in part due to improper use of experts and improper procedures employed by expert witnesses. Other judicial abuses and hysteria contributed to the injustice in addition to questionable expert witnesses. However, it is fair to say the professionals and expert witnesses added to the hysteria that surrounded the trial. Following is a link to an article by Lew Powell concerning the case. Little Rascals Daycare


We often defer to experts and people in lab coats. However, expert witnesses offer opinions, not facts. Testimony from expert witnesses for the prosecution can be challenged. First, the expert witness must have the proper credentials. Also, expertise in one matter does not mean the expert witness is qualified in a second area.

Expert witnesses must follow the proper protocol. The protocol includes numerous issues. A conscientious Phoenix defense attorney will research the protocol and fight to keep out testimony that was not prepared according to it. Moreover, expert witnesses are human. Consequently, they are subject to intentional misbehavior and biases.

Howard Snader is not intimidated by prosecution experts. He will investigate and ask them the tough questions. Call today to schedule an appointment.