7 Keys to a Winning Direct Examination of an Expert Witness

7 Keys to a Winning Direct Examination of an Expert Witness

An expert witness has a unique opportunity to truly shine and score extra points that could mean the difference between a win or a loss in your competition. Here is what you should do to maximize this opportunity.

1. Understand the Difference Between an Expert Witness and a Lay Witness

A lay witness can only testify to facts they have personal knowledge about, so they must have directly experienced before they can testify to it. In contrast, an expert witness can form an opinion based on facts that they did not personally experience, as long as those facts come from a source that is reliable and is of a kind that professionals in that field typically rely.

For example, you’re an expert in pathology who’s being asked for an opinion on the victim’s cause of death. Because it’s unlikely that a pathologist will happen to be around to witness a murder, pathologists may rely on things like police reports to find out what happened on the day of the crime. So it’s fair for you to rely on the facts in a police report when you form your opinion.

Expert witnesses have some kind of specialized knowledge that your average person won’t have. Typically, this is a field that is technical and/or that requires special education or experience, such as medicine, psychology, or linguistics. An expert opinion is based in part on this specialized knowledge.

But a lay opinion is based on knowledge and experience that a typical person has. For example, a lay witness can testify that they saw the defendant looking angry. They don’t need a psychology degree or expertise to make that assessment. They can tell the defendant looked angry based on what the defendant’s appearance and actions, like he was red in the face, slamming doors shut, and yelling.

2. Determine When to Call Your Expert

It’s best if your team presents evidence of the facts your expert assumes, before your expert testifies. For example, if your expert opines that the victim’s cause of death is the gunshot wound to his chest, you need someone to first testify that the victim actually suffered a gunshot wound. This helps your audience follow along with your theory and understand how your expert fits in with your case.

3:   Make an Impact in the First 15 Seconds of the Direct Examination

Give your audience an idea of who this witness is and how they fit in with your case. There are three elements to discuss in the first few questions of your expert’s direct examination.

a. Expert Qualifications

This can include your expert’s:

  • education,
  • professional career,
  • any published scholarly articles or textbooks,
  • special awards they’ve received,
  • any teaching experience they have, and
  • previous experience testifying as an expert witness.

Basically, you want to show the judge that your expert is an authority in their field and that they have more knowledge and experience in the field than a regular, everyday person.

b. Factual Assumptions


  • What are the facts about this case that your expert assumes so that they can form their opinion?
  • Where does your expert get these facts from?
  • Why are those sources reliable?

c. Expert Opinion(s)

The most important part of the direct examination of an expert witness is the expert’s opinion, which will help the judge decide whether the defendant is guilty.

Here is a sample that shows how you can use the first few questions of an expert’s direct exam to briefly identify their background, factual assumptions, and opinions:

Q:  Dr. Peters, please introduce yourself to the Court.

A:  I am a pathologist and have been the state’s Chief Medical Examiner for the last ten years.

Q:  What’s your involvement in this case?

A:  I was asked by the prosecution to determine the victim’s cause of death.

Q:  What materials, if any, did you review?

A:  I reviewed the police report and photographs of the victim’s gunshot sound.

Q:  Did you form any opinions in this case?

A:  Yes, I formed three opinions.

Q:  Can you please list those opinions?

A:  My first opinion is __. My second opinion is __. And my third opinion is ___. [Have your witness express these opinions in as few words as possible.]

4. Give Details About Your Expert’s Qualifications

In real-life trials, attorneys have to show that their expert witness really is an expert with proper qualifications. They then have to ask the judge to deem the witness an expert witness.

In some mock trial competitions (including California high school mock trial), you don’t need to go through this process because the prosecution and defense stipulate (agree) that the expert witnesses are qualified expert witnesses.

But, even if it’s been stipulated that your expert witness is properly qualified, your expert should still describe their background to demonstrate their ability. This is to show that the expert is awesome and that the judge should believe them, not the opposing expert.

After the expert witness describes why they are so awesome, you should also address any potential attacks on the expert’s credibility. Some might be:

  • The witness is a “professional expert”, rather than one who has a professional practice;
  • The witness has a record of always working on the same side of the case (e.g., always works with the prosecution); or
  • The witness is fairly new in their field of expertise.

If there are attacks on your expert’s credibility, don’t just hope opposing counsel won’t bring them up. Deal with them on direct examination. This is better than having these facts presented for the first time during cross-examination, and then appearing defensive when you address the attacks during re-direct.

Discuss the potentially negative facts, and then shine a positive light on your expert. For example, maybe your witness is new to the field, but has won a prestigious award.

5. Educate Your Audience

If you are an expert witness, you should – for each of your expert opinions – state the facts that form the basis of your opinion and the methodology you used. This is how you can truly shine as a witness.

As an expert witness, you are educating the judge and your audience. You have special knowledge, background, and experience in a field that most people know nothing about. You should explain these technical, complex issues in a way that makes sense for just about anyone.

Tips for An Amazing Expert Witnesses Performance

Tip # 1: Develop Your Character

How do you want to fill your role as an educator? Think about:

  • How do you want to appear on the stand?
  • What’s your demeanor like?
    • Are you going to be like a professor – serious and heavy on the jargon?
    • Or are you going to be more of a celebrity personality, like a coach in a reality TV competition?
    • Or will you take on another kind of personality?
  • Are you going to come across as a bit condescending and like a know-it-all (common for expert witnesses), or are you going to be more approachable?

Tip # 2: Use Your Own Words, Instead of Just Re-Stating Their Witness Statement

During your direct examination, you should use your own words as much as possible to explain the technical concepts. Often in mock trial, expert witnesses basically regurgitate full sentences from their witness statement, word for word. This is missing a huge opportunity. (It’s also kind of boring to listen to.)

But if you show that you’ve really understood and analyzed the complex expert issues, and are able to explain them in a unique way, you can get a perfect score.

Tip # 3:  Use Examples to Explain Technical Concepts

You should come up with analogies and real-life examples to demonstrate the concepts you are discussing and get the audience interested in them.

Say you’re a pathology expert testifying that the victim died because of a chronic disease, not because of the gunshot wound allegedly inflicted by the defendant. You might use the analogy of a dilapidated building that collapsed during a minor earthquake. You would say that the building’s structure was failing and that is why it fell; the occurrence of the earthquake was coincidental. You would then explain that similarly, the victim died because of his disease, and that the gunshot wound he suffered was unfortunate but had no part in his death.

Tip # 4: Ask the Expert to Explain Jargon and Technical Terms

Since the expert is so immersed in their field, they might not even recognize they’re using jargon and technical terms. So, if you are an attorney conducting the direct examination of a witness, be sure to ask questions such as:

  • What do you mean when you say [technical term or phrase]?
  • What’s the significance of [the location of the gunshot wound]?
  • Would you explain what you mean by [a chronic disease].

Asking these questions gives the expert a chance to show off their expertise and explain these concepts to the audience.

6. Show Why Your Expert Witness is More Credible Than Your Opponent’s

If you’re an expert witness, you shouldn’t come out and say, “I’m a better expert than the other guy! Believe me, not him!”  But you should leave the judge thinking exactly this.

As an expert, you’ll reach a different conclusion than your opposing expert, but there may be one or two things you agree on, such as facts or methodologies. You may even share an opinion or part of an opinion. That’s a good thing. It adds to your credibility when you can admit that the opposing expert got at least some parts of the analysis right.

You’ll then explain the ways your opinion differs from the opposing expert’s. As you do this, explain why your factual assumptions and/or methodologies are better or more reliable than the opposing expert’s. (In other words, the bases for your opinion is more reliable, therefore, your opinion is better.)

This portion of the direct exam might look like:

Q: Have you reviewed Dr. Peters’s work in this case?

A:  Yes, I have.

Q:  Did you agree with it?

A:  Yes and no.

Q:  What did you agree with?

A: [witness response]

Q:  What did you disagree with?

7. End With A Powerful “Take Home” Statement

What’s the one main point your expert contributes to your case theory?  The last thing an expert says during their direct exam should answer that question for your audience.

Sample wrap-up questions for your expert’s direct examination are:

  • Based on everything you’ve testified to this evening, what is the victim’s cause of death?
  • In light of the facts, methodologies, and opinions you described this evening, what is the cause of the victim’s death?

Try a variation of these questions to help your audience grasp how your expert’s opinion fits in with the case you are presenting.


The direct examination of an expert witness is a huge opportunity for your witness to shine and score big points with your audience. To make the most of this opportunity, use the seven keys I’ve described in this article. For your easy reference, I’ve put together the checklist below for you to refer to as you prepare your expert’s direct examination.

Direct Examination of Expert Witness
7 Keys to Direct Examination of Expert Witness