In criminal law expert witnesses may play a critical role in defending a case.
What is an expert witness? What can expert witnesses say at trial? What can’t they say? How will an expert witness help me defend my case?
What is an expert witness?
An expert witness can testify about perceptions but also an opinion within their expertise. An expert witness provides the judge and jury with scientific, technical, or other specialized knowledge. Their role is to provide the court with unbiased information on something the average person is unlikely to understand on their own.
What are some examples of expert witnesses?
There is a very wide range of issues an expert witness can testify on. Here is a list of four of the most commonly used expert witnesses for defendants in criminal cases:
Medical and Mental Health Experts: Medical experts include doctors, nurses, physical therapists, or any other person with a medical education. In criminal cases they are often called to testify about injuries, addictions, and deaths as well as treatments. Medical experts also include mental health experts, like psychologists and psychiatrists, who will speak on a person’s state of mind and any mental health defects impacting their intent or understanding of what they were doing. Certain defenses, like the insanity defense, can dependent heavily on expert opinion on a defendant’s state of mind.
Engineer and Vocational Experts: Vocational experts are people with qualifications in a specific type of job or profession. They could include licensed mechanics, electricians, or heating and ventilation specialists. In criminal cases they might speak to how a motor vehicle or piece of equipment was operating on a particular day or generally.
Forensic Experts: Forensic experts testify about matters involving the forensic sciences. Forensics is not limited to DNAand genetics. Forensics also includes how firearms are operated and how data is collected in bulk.
Financial Experts: If a person is accused of a financial crime like fraud the defense might call a financial expert to testify on how a particular financial transaction occurred or what is normal and ethical practice in the financial world.
What won’t an expert witness do?
Although lawyers consult with and compensate expert witnesses for their testimony on behalf of a client an expert witness is technically not an advocate. In other words, they are supposed to provide an honest and unbiased professional opinion on an issue.
An expert also must only testify on the issue they are competent to testify on. Competency usually means having a professional license or title or being distinguished in a particular area. For example, a court won’t allow an expert witness who is hired for their expertise on mental health to testify on the stand about something totally unrelated to mental health, such as whether or not a driver was driving safely on a particular day.
Finally, an expert witness is not allowed to provide legal advice or to act as a negotiator. Lawyers help clients make informed legal decisions. Making an informed legal decision means looking at the strength of the evidence. While lawyers can and should rely on expert opinions on the strength of evidence the final decision as to if a legal decision should be made is between the client and their attorney.
How could an expert witness help my case?
There are many complicated court rules on who is allowed to testify as an expert witness and what matters they may testify on. If your case is headed for trial it is your lawyer’s job to help you navigate these rules and also select the best possible expert witnesses for your position.
More generally, what an expert says on the stand is evidence. Evidence is ultimately what decides a case. In order for any person to be convicted of a crime the government must prove them guilty beyond a reasonable doubt. Where there is insufficient evidence, an accused person cannot be convicted. More importantly, when the government presents evidence suggesting that a person may be guilty an expert witness may help to cast doubt on that evidence. If the jury becomes reasonably doubtful that the accused person committed a crime they are required by law to acquit.
To put it another way, an expert witness can be so important that it can make the difference between an accused person walking away and losing their liberty.
IF YOU OR A LOVED ONE THINK YOU MAY NEED THE ASSISTANCE OF AN EXPERT WITNESS IN A CRIMINAL CASE, AND YOU NEED AN EXPERIENCED CRIMINAL DEFENSE LAWYER WORKING ON YOUR SIDE TO PROTECT YOUR RIGHTS, PLEASE CONTACT CRIMINAL DEFENSE ATTORNEY WILLIAM J. BARABINO.
CALL 781-393-5900 TO LEARN MORE ABOUT YOUR AVAILABLE DEFENSES.