Knowledge is Power: How to Use Expert Witnesses in Your Case

Many issues need to be argued and established in a criminal defense case. Some cases are defended by the concrete facts alone, while others hinge upon the fact that law enforcement did not follow protocol.

Most other cases fall somewhere in between. Both prosecutors and criminal defense lawyers in New Mexico will use expert witnesses to argue these gray areas.

Experts play an essential role in civil and criminal trials. When defending a criminal charge, there are times I need the judge or jury to decide on the correctness of the matter.

It’s not enough for me to say, “Trust me on this. The police didn’t do this correctly. My client is not guilty.” I need to show why what they did was wrong by using the opinion of an expert.

In This Post

In this post, I help you understand what expert witnesses are, why they are important, and how one New York defendant used them to his advantage.

What Is Expert Witness Testimony?

Under the state’s rules of evidence, a witness is qualified as an expert by establishing his or her knowledge, skill, experience, training, or education in a particular field. That person can give an opinion, help the judge or jury understand the evidence, or decide a disputed fact by using his or her testimony.

Expert Testimony Is Refutable

The opposing side can challenge whether the person should be considered an expert. Expert witnesses can earn substantial incomes. A defense attorney could also make the expert look biased and his testimony untrustworthy if it’s shown the person has testified in many trials making opinions friendly to prosecutors.

Expert witness testimony doesn’t have to be taken as gospel because he or she is an “expert.” The judge or jury members can believe or not believe what’s said, partially or totally. Although expert witness testimony is used in all kinds of criminal trials, they can be especially helpful in DWI/DUI cases.

There’s a multi-step process that must be followed in DWI/DUI cases. Whether or not law enforcement acted appropriately and had a valid basis for an arrest can be a topic of expert witness testimony.

Example: Improperly Performed Tests Result in an Illegal Arrest

A New York case is a good example. Avriel Hillman was arrested in 2018 for driving while intoxicated. At her trial, police officer Peter Carcaterra testified he witnessed erratic driving and pulled Hillman over.

He testified that he smelled alcohol from her breath; her eyes were bloodshot and watery. Hillman also admitted she had an alcoholic drink earlier that night.

Officer Elena Cotto joined them at the scene. Hillman participated in three standardized field sobriety tests (SFST’s): the horizontal gaze nystagmus test (HGN), the walk-and-turn test, and the one-leg stand test.

Carcaterra thought she failed all three tests. Hillman was arrested and had her breath tested at the police station. The results were that her blood alcohol level was above the legal limit.

At a pre-trial hearing, the defendant’s expert witness in SFST’s, Anthony Palacios, argued they were not administered correctly. Without valid evidence from the tests, there was no legal basis for the arrest.

Palacios testified:


This involves involuntary movements of the eye and how much they may be affected by alcohol and or drugs. The suspect is to follow an object, one eye at a time (not moving the head) to the left and right. The officer looks for the angle where the pupil starts to move involuntarily.

If it happens early (at or before a 45-degree angle), it’s supposed to be a sign the person is intoxicated. Palacios, basing his opinion on the dashcam video of the testing, stated the HGN wasn’t given correctly.

The object should be just above eye level, but Carcaterra held it above her head. He also did the test too quickly. Palacios stated that because of these problems, test results weren’t reliable evidence of intoxication.

Physical Agility Tests

Hillman suffered from a condition that resulted in one leg being longer than the other. She used a crutch to walk.

Palacios testified those with leg problems shouldn’t be asked to stand on one leg or walk and turn to determine if they’re intoxicated or not. They could do the best they could sober and move in a way that makes them look impaired

The judge agreed with Palacios. He found that the test results were invalid. The judge also found dashcam video didn’t show Hillman drove erratically, as Carcaterra claimed.

Because of these problems, Hillman’s arrest was illegal. Breath test evidence and statements by Hillman also couldn’t be used by the prosecution, so the charges were dismissed.

The Difference Between Freedom and Conviction

Like the Hillman case, we use expert witnesses to tell the stories that need to be told: charges should be dismissed, prosecution evidence should be suppressed, and our client is not guilty. An expert witness could be the difference between freedom and conviction.

Call for a FREE Strategy Session

If you’ve been arrested, stand up and fight for yourself by talking to a Las Vegas, New Mexico criminal defense lawyer who can assess your situation and give you the unbiased answers that you need.

Contact Grano Law Offices, P.C., for a free strategy session today by calling 505-587-8649 or by sending me a private message here.

I respond to most messages within a few hours but may take up to the next business day to receive a response from me.

Posted in Criminal Defense

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