The Different Types of Witnesses

In litigation, lawyers rely on the testimony of witnesses in order to present their case. Lay witnesses, which are the most common kind of witnesses, are individuals who have knowledge about certain events and will describe what they know in connection to the case. Character witnesses are people who know a party in the case, either the victim or the defendant, and can testify to the positive or negative character traits and reputation of that individual. Expert witnesses are a unique asset to a lawyer’s case. An expert witness does not need to witness certain events or testify to an individual’s character. In fact, expert witnesses do not need to know any party in the case prior to being retained. Expert witnesses are “specialists” – those who are educated and experienced in a certain area. These witnesses are permitted to testify, and offer opinions with regard to the case at hand, based on their specializations pursuant to Federal Rule of Evidence (FRE) 702:

Rule 702. Testimony by Expert Witnesses

A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if:

(a) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue;

(b) the testimony is based on sufficient facts or data;

(c) the testimony is the product of reliable principles and methods; and

(d) the expert has reliably applied the principles and methods to the facts of the case.

There are a plethora of different types of expert witnesses ranging from medical experts, forensic experts, engineering experts, financial experts, and more. While expert witnesses can be an incredible asset to your case they are also, arguably, the most intimidating. How do you guide an expert and elicit particular answers in your favor when the expert witness has more knowledge than you on the subject matter? How do you conduct a cross-examination of an expert witness and persuade a judge or jury that the witness’ conclusion or opinion is wrong, when they are the expert, and you are simply the advocate? These were the challenges I personally faced when I was asked to participate in the 2022 Hofstra Legal-Medical Mock Trial Competition.

This particular mock trial competition was unique in that each team was provided with a lay witness from Hofstra, as well as a medical student to play an expert witness from the Zucker School of Medicine at Hofstra.

The two experts used in this year’s competition were a Toxicologist/Pathologist for the plaintiff, and a Cardiologist for the defense. As an advocate for the defense, it was my goal to persuade the jury in this wrongful death case that the victim did not die as a result of acute alcohol intoxication which led to death by trauma, but instead the cause of death was an underlying heart condition called hypertrophic obstructive cardiomyopathy which led to a secondary ventricular arrhythmia. If you had to read that sentence more than once to figure out how to pronounce those medical terms, and try to understand what they may mean, that is exactly how a jury feels when they are presented with these complex terms for the very first time. Think if you went to your doctor and they told you you had a condition. The condition might be one which you have never heard of before, and even if you had heard of the condition, you are likely to ask follow up questions; what does that mean, where did this come from, why does this happen, how can I treat it, etc,. These questions don’t just apply to the medical field either; a contractor building a house can tell you construction needs to build something one way or another, and you are likely going to ask why. A financial advisor can inform you to invest your money in certain places and not others, and you will have certain follow up questions. When the typical “lay” person[1] does not have enough knowledge and experience in a particular field, they are going to seek opinions from individuals with extensive knowledge and experience to help them better understand. That is exactly what expert witnesses are used for during trials. Yes, expert witnesses can be extremely intimidating, especially for new lawyers, or lawyers who have never examined an expert witness before. Getting comfortable with an expert witness takes time and experience, however if you keep the following tips and tricks in mind, you will have no trouble mastering the direct and the cross examinations of an expert witness.

General Guidance

This should go without saying, but prepare and do the extra research. Preparation is KEY in litigation, as trials are won and lost based on the preparation you put into your case. Preparation in general extends to understanding your theory, your theme, knowing the facts that help you, and acknowledging the facts or issues that may hurt you. The extra research that comes with utilizing an expert witness is understanding not only the opinion your expert witness is going to provide, but the opinion of an opposing party expert, and how they reached that opinion. You not only need to understand the opinion they are offering, but you need to understand the substance surrounding their opinion. The research into the information an expert witness is going to be testifying to is imperative for several reasons. First, it provides a sense of confidence when it comes to the direct and cross examination. When you have a general understanding regarding what the expert witness is going to be testifying to, you not only ask your questions with more confidence, but you are able to ask the appropriate follow up questions if you notice they left a detail out in their answer that you feel the jury needs to have a complete understanding of the testimony.

Second, research will provide a smoother preparation process with your expert witness. In conducting your own research, you are bound to have several questions regarding the subject area this witness is going to testify to. In preparing questions, you are going to receive answers from your expert witness that will offer in-depth explanations that not only enhance your understanding of the subject matter, but provide detail you can then apply to the facts of your case. The questions you have will also help you create a roadmap, especially for your direct examination, to ensure the appropriate questions are asked that will make the testimony understandable to the average juror. Do not feel intimidated to ask your expert witness questions, because ultimately experts know the subject matter, but you know the law. Experts are used for a specific purpose, but the attorney is the one who knows all of the details surrounding the entirety of the case. In asking your questions, you can provide them context from other details within the case that they may not be privy to in order to explain your understanding. The same way you, as the attorney, rely on the expert’s knowledge to support your case theory, experts rely on you to have knowledge of all of the facts that will allow them to come to a reasonable conclusion. This also applies to cross-examination; while the expert has knowledge in the opposing side’s case theory, you are the one who knows all of the details in the case, conducted your own research and know what to ask in order to poke holes in their opinion. Now what happens when you get to trial and how do you best utilize the expert witness?

The Direct Examination

When you are directing an expert witness, it is imperative that you create a foundation for this witness to testify to a specific subject matter and offer testimony in the form of an opinion. The first portion of your expert’s direct examination is the expert tendering, otherwise known as the voir dire. A key takeaway to a voir dire is to present appropriate background before offering the expert’s opinion. An opinion by an expert cannot be offered until the witness is tendered, but what information is required to tender the expert? There is a tendency to offer every piece of information regarding the expert witness’ education, employment history, certifications, licenses, publications, achievements, awards and honors in order to tender them. The more information you elicit, the longer your voir dire is going to be and the likelihood of you losing a jury’s interest increases severely. As an attorney, you should find the best information to qualify your witness as an expert and offer that information in the shortest amount of time. If I were to rank qualifying information; education, experience, and licenses/certifications are arguably the most important pieces of information as it provides context to support the expert’s scientific, technical, or other specialized knowledge for the subject area they are going to testify to. All of this is imperative to qualifying them as an expert under FRE 702.

Once you get past the voir dire, and your witness is tendered as an expert, the remainder of your direct examination is to have the expert witness explain the scientific, technical, or other specialized knowledge/data to support how they reached their overall conclusion. Think of an expert’s direct-examination like baking a cake; your overall goal is to bake a cake and in order to do this, you have to have all of your ingredients and follow recipe instructions. If you are missing an ingredient, or skip a step in the recipe you are not going to have your “ideal” cake. The expert’s specialized knowledge, and the details and facts within your case are the ingredients. The questions you ask during direct examination are your recipe. Your end goal is to have the jury understand and agree with your expert’s overall testimony, and since you have all of your “ingredients,” you must create a clear and thorough “recipe” that utilizes all of the important “ingredients” to get to your end goal.

The only way you can effectively walk a jury through understanding the expert witness’ testimony is to simplify EVERYTHING. Expert witnesses tend to use advanced language when offering testimony, and if you do not break down the testimony, the jury is not going to follow and understand the points you want the witness to make. For example, my witness in the legal-medical competition testified that the victim suffered from a condition known as “HCOM”. My direct examination broke down, into simple layman’s terms, what this condition was, how this condition affects the individual who suffers from it, different levels of severity, and treatment options. The second portion of my witness’s conclusion was that this condition led to ventricular arrhythmia. When I first read about ventricular arrhythmia, I had no idea what it was. It was not until asking my witness the appropriate follow up question of “what is ventricular arrhythmia” that I learned it is just the fancy medical term for a type of cardiac arrest (aka, a heart attack). The key to knowing if you need to break down an answer is to constantly ask yourself; if I did not do any outside research, do I understand what that answer means? If the answer is yes, move on. If the answer is no, think about what the average juror may not understand and ask the appropriate follow up question. If an expert testifies that “something” happens, break it down by asking how it happens, and why it happens. Once you break down all of the complex information, always remember to bring it back to your case and how this information justifies your case theory.

In addition to breaking down complex testimony, another effective tool to master the direct examination of an expert witness is to use demonstratives to explain major points. Demonstratives are visual aids, which are an effective tool in examining any witness, but since expert testimony can be far more complex, take advantage of demonstratives. Visuals do not have to be photographs, or reports that could be used by any other witness. Demonstratives can be timelines, flow charts, or other visual aids that break down the expert’s testimony and give the jury something to reference and remember what your expert testified to when they deliberate. Overall, the simpler you can make the content of the examination, the easier it will be to examine your expert witness.

The Cross Examination

The cross examination of an expert witness is arguably the riskiest part of a trial if you are faced with an opposing party expert. On one hand, you run the risk of run around answers when it comes to experts. For example, you can have an issue where one expert views the issue in one light, and another expert views it differently. When you are attempting to elicit an opinion or fact that is most favorable to you, the expert you are questioning can say “well it depends” or “not necessarily” and continue with a long winded explanation as to why the answer you were looking for is not necessarily the case. When you get those kinds of answers you’ve now allowed the jury to hear information that potentially discredits your case theory and bolsters the other side. A key to cross examination is to ask leading questions that elicit a yes or no answer (in addition to the fact that you should never ask a question you don’t know the answer to). Cross examination of an expert becomes tricky because you may elicit more than just a yes or no answer as the subject matter and content to which an expert will testify to is a little more technical and advanced than facts and issues with a lay witness. Additionally receiving run around responses can have a tendency to throw you off. On cross-examination, you should always control your witness and never let a witness control you, and if you let a witness throw you off a judge and/or jury will be able to see that instantly.

There is also this tendency, with cross-examination in general, for attorneys to stand up for cross and instantly attack the witness in order to enhance their own case theory by making the witness on the stand look bad. The first time I conducted a cross examination of an expert witness was during an internal team scrimmage of the 2021 Hofstra Legal-Medical Mock Trial Competition fact pattern. When I concluded my cross examination I sat down and felt great; the witness tried to smack me around but I stood my ground and shut them down the best I could. Instantly, my coach’s feedback was “slow down Rocky,” making a reference to the movie Rocky III when Rocky fights Clubber and comes out swinging fast and aggressive during the championship fight.[2] At first I didn’t feel as though my cross examination was aggressive. It was not until I watched the recording back that I realized I was extremely overzealous and I needed to reconsider my approach to the cross examination in order to “look good” in front of the jury while getting my point across.

In reconsidering my approach, I observed the examination of one of my teammates who was conducting the cross examination of my expert witness. In analyzing my teammates’ talented approach to the expert cross, I quickly learned one of the most valuable lessons to mastering the cross examination of an expert which is to get the expert you are crossing to agree with your case theory. Unless you are successful in precluding an expert witness from being tendered as an expert, their relevant conclusions and opinions are coming in. It is very difficult to then attempt to attack an expert witness’s testimony as they are the ones with the specialized knowledge and more times than not, will offer lengthy explanations when you attempt to discredit them. If your case theory is supported by facts they are authorized to testify to as an expert, have them agree with certain facts that are favorable to you. Oftentimes, things the expert witness can agree to on cross, are points they may have disregarded when coming to their own conclusion. The subtle attack of an expert witness is done when you can have them agree with you on certain points, show the jury that they disregarded these points in coming to their own conclusions, and had they considered the points that you just had them agree with, they may have come to a different conclusion; a conclusion that could have been in your favor.

This leads me to another tactic to utilize on the cross-examination of an expert; if the facts of the case allow, attack what they assume to be true. As I previously mentioned, while expert witnesses have specialized knowledge in a certain area, they rely on the lawyers who retained them to provide them with the details of the entire case. It would be ignorant to assume that biases do not exist, especially when it comes to expert witnesses, as at the end of the day, they are getting paid by the party they are testifying on behalf of. They are prepared and provided information by the opposing party which leads to the potential assumption of facts that your adversary wishes to be true. For example, in the Hofstra Legal-Medical Competition, the plaintiff’s contention was that the victim consumed an excessive amount of alcohol which led to a blood alcohol content (BAC) of .24 at his time of death. It was the plaintiff’s expert’s contention that this heightened BAC led to a series of side effects including impaired motor function and loss of consciousness that led to his ultimate death by trauma. The victim’s BAC was supported by a toxicology report, and the link between alcohol consumption and the defendant was the fact that the defendant was a fraternity and they shared a “beer olympics” rule and schedule sheet. These rules and schedule sheet laid out how much alcohol was meant to be consumed by the competitors and when. Now when reading those facts, it appears to be an incredibly strong case made by the expert witness. However, the beer olympics rules sheet was general – no one could state for certain the actual requirement of each participant to consume all of the alcohol listed in the rules. There were also no witnesses who could state that they saw the victim consuming all of this alcohol. With his blood alcohol level, there was no disputing he did consume alcohol, however no one was ever able to confirm that they saw the victim in the case so intoxicated that he was falling in and out of consciousness. This was a fact assumed to be true by the expert witness which he confirmed to be assumed on cross examination. Attacking what an expert assumes to be true can ultimately discredit their overall opinion, as their opinion may not be as strongly supported as originally portrayed.

One final tactic to mastering the expert cross-examination is, if applicable, utilize learned treatises; learned Treatises are your secret weapon and your best friend. A learned treatise refers to a legal doctrine establishing a published text as authoritative, either by expert testimony or by judicial notice, and it serves as an exception to the hearsay rule[3]. Learned treatises are typically journals or articles from a source that is typically relied upon in that expert’s field. In utilizing a learned treatise, you can find a fact or statistic that may contradict a point the expert witness is testifying to. How this aids your case is that learned treatises are judicially noted, and it is difficult for the expert to then dispute the point you are making in your learned treatise. Even if the expert attempts to give you a run around answer regarding how the information you are presented through the learned treatise may not apply in this case, the opportunity you have to present the potential for this fact to be true in the case at hand is still present. Through a learned treatise, you are still given the opportunity to discreetly attack and discredit the expert’s opinion and testimony.

Ultimately, examining an expert witness is difficult. It can take a lot of time and experience in order for you to get comfortable direct or cross examining an expert witness. I speak simply from mock trial experience – the first time I was nervous, intimidated, and didn’t think I would be able to do it successfully. With the experience I gained, and what I learned in preparation for this mock trial competition, I can confidently say that I would be comfortable direct and/or cross examining an expert witness at any point in my legal career. The experience I had, and the lessons I learned were shared here, in hopes that I can provide other attorneys a sense of comfort and guidance when they are tasked with utilizing an expert witness.

[1] The term ‘lay people’ is used to describe the use of ordinary, non-qualified people in the legal system.


[3] Inc. US Legal, Learned-Treatise Rule Law and Legal Definition | USLegal, Inc., (last visited Nov 29, 2022).