The very first obstacle a prosecutor must overcome is the test for relevancy. In other words, one must ask "Does the witness's testimony tend to prove or negate the issues present in the case?" If a witness's testimony is NOT relevant to the issues at hand, he/she may not testify.
This is extremely important because prosecutors will routinely try to admit the testimony of people who are not relevant to the issues, to help bolster their case. For example, the prosecution in a domestic violence case is not permitted to introduce testimony that the defendant has a criminal record for DUI.
The fact that a criminal defendant may or may not have operated a motor vehicle at some time in the past, while impaired, has absolutely no bearing on whether or not he slapped his wife across the face in an unrelated incident.
Thus, a witness's testimony must be relevant, if it is to be admitted in court.
Is the Witness Testimony Credible?
After relevancy, a criminal defense lawyer must next consider whether or not a potential witness has credibility problems. A witness may lack credibility if he/she has given inconsistent statements, makes incredulous claims, or is otherwise proven to be unreliable.
A criminal defense lawyer must determine whether or not the witness was in a position to make the observations he/she is testifying about. Likewise, it is equally important to find out if the witness made his/her observations in context.
In other words, even if we were to assume the witness is honest, is there any other reason to doubt what he/she is saying? For example, if a witness claims to identify an attacker and it is determined that the witness's only observation of the alleged attacker was made from across the street, as the defendant drove by in a moving vehicle with tinted windows, the witness's belief that he saw a person matching the defendant's description may be suspect.
Does Other Evidence Contradict the Witness's Testimony?
Even when people testify to the best of their ability and tell the truth, that does not mean they are correct in their assertions. Sometimes people are mistaken about what they observe. Such mistakes can occur because of environmental factors, such as darkness or rain, physical limitations like poor eyesight, situation stress, or simply from a lack of paying attention.
When a person is being prosecuted for a crime, his/her freedom is at stake. For this reason, it is imperative for a criminal defense lawyer to flush out every possible reason why a witness may be mistaken, even when the witness is an honest witness.
To accomplish this, a criminal defense lawyer may look to other evidence in the case. For example, do the witnesses give varying accounts of what happened? In the alternative, do different witnesses give different descriptions of the suspect?
Ultimately, all testimony and evidence must be read in context to make sure they are harmonious and not contradictory.
Expert Witness Testimony
Generally speaking, witnesses may only opine about matters that are knowable by a lay person. For example, a person may estimate the speed of a moving car without being accepted by the court as an expert in physics.
However, before an opinion about non-lay matters may be given, a witness must be accepted by the court as an expert. Additionally, an expert witness may only render opinions on matters that he/she has been accepted as an expert in.
For example, a fingerprint expert is not permitted to testify about cause of death because such an opinion is clearly outside the realm of fingerprint evidence.
Like other testimony, an expert witness is also subject to the relevancy test. Not only must the witness's area of expertise be relevant, but the subject matter of his/her opinion must also be relevant.
Expert testimony must also be credible. Determining whether or not it is consistent with other evidence or other expert testimony is equally important.
While this guide was not intended to be comprehensive, it was meant to direct the reader's attention to some of the most important issues present when dealing with witness testimony. When a person is prosecuted for a criminal offense, his/her freedom and reputation is at stake.
For that reason, a criminal defense lawyer must diligently address each of the claims made by the prosecution's witnesses. Such claims must be checked for relevance, credibility, integrity, and consistency. By challenging witness testimony in this way, a criminal defense lawyer is able to uncover latent defenses that can be used for the client's benefit.
In some cases, uncovering such defenses can make the difference between a wrong conviction and justice.
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