Marisa Tomei From My Cousin Vinny Great Example Of How An Expert Witness Works

Whala! My Cousin Vinny, Mona Testifies as an Expert Witness

The expert witness defined by Marisa Tomei is credible. Remember that scene from My Cousin Vinny where Attorney Frank Gambini (Joe Pesci) calls his finace, Mona Lisa Vito, to the witness stand to testify in the murder trial of his cousin?

She did alright on the stand, didn’t she? I would  give a pinky toe to have as effective an expert witness as Mona Lisa Vito testify in my next jury trial.  I don’t believe  I’ve ever finished a direct examination of an expert witness with the question, “She’s cute too, hugh?”

Mona on the Stand: Expert Witness Defined by Marisa Tomei
Gambini: May I have permission to treat Ms. Vito as a hostile witness?
Mona: You think I’m hostile now, wait till you see me tonight.

Did you wonder if it was possible for a defense attorney to call a witness, so easily like that,  even when the witness has nothing to do with the case; and is his finance? The short answer is “yes” because the criminal law distinguishes between occurrence witnesses (also called lay witnesses) and expert witnesses. You can think of an occurrence witness as a person who knows something about the the case because they experienced something. Eyewitnesses and victims of crime are great examples of occurrence witnesses.

Opinion Testimony

The criminal rules are very strict about letting occurrence witness testify about their opinions concerning important issues in the case. Lay witness opinion testimony is going to be very limited and narrow in scope. For example, a victim’s mother is not going to be allowed to testify about her opinion on why the “good for nothing” boyfriend cannot be trusted. This rule of evidence is so important that convictions and long prison sentences can get overturned if a judge thinks improper opinion testimony entered into a case.

But the rule is different with an expert witness. Expert witnesses actually are allowed to give their opinion about important aspects in the case. In fact, the only reason to really call an expert witness is for his or her opinion on something really important in a case.

Expert Witness Testimony

For example, Federal Rule of Evidence 702 states that:

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.

This means that when a proponent of an expert witness can establish the required “foundation” for that expert, the court is going to allow that witness to testify about their opinion. Obviously, the witness will have an opinion based on their particular expertise. Expert witnesses are not allowed to get on the stand to testify about any opinion they have. It would be just as objectionable to call an “expert” witness just to tell the court that the victim’s boyfriend truly is a “good for nothing.”

Mona testified as an expert in the field of automotives, and she limited her opinion testimony to that area of expertise. Thus, the expert witness defined by Marisa Tomei was done legally and credibly. 

Learn more about the Illinois Rules of Evidence.

Laying a Foundation

Getting back to “foundation,” what we mean by “foundation” is that the expert witness satisfies the points made in Rule 702.

The custom in a trial is that the expert witness takes the stand to first answer answer questions about their qualifications as an expert. If the judge and the opposing counsel are satisfied then the witness continues to testify about what her opinion in the case happens to be. This process is called a voir dire of the witness. This just means that either the judge or the attorneys are allowed to ask questions to establish, or not establish, the qualifications of the expert. If a witness does not get passed voir dire they will not be allowed to testify any further. See also Qualifying the Expert Witness: A Practical Voir Dire.

If you look carefully at Rule 702, it actually does not spell out a specific protocol to become an expert witness. No specific degree or education is required. Yes, having a college degree or advanced degree can be one way to establish expertise as an expert witness, but it is not the only way. Mona developed her expertise by working in her father’s garage. Police are routinely qualified as expert witness merely from their day to day experiences as police officers.

Expert Witness Defined by Marisa Tomei

In My Cousin Vinny, Mona’s voir dire and explanation of her expertise went like this:

Gambini (G): Your Honor, the defense calls as its first witness Miss Mona Lisa Vito.

Prosecution (P): I object your Honor, this person ‘s not on the witness list.

G: This witness is an expert in the field of automobiles, and is being called to rebut the testimony of George Wilbur.

Judge (J): Officer?

G: Would you please instruct the officer to escort Miss Vito to the witness stand please?

Bailiff: Hold up your right hand. Do you swear to tell the truth, the whole truth and nothing but the truth so help you god?

Mona (M): Yeah.

G: Miss Vito, you’re supposed to be some kind of expert in automobiles, is that correct? Is that correct?

[No answer]

J: Will you please answer the Counselor’s question?

M: No, I hate him.

G: May I have permission to treat Miss Vito as a hostile witness?

M: You think I’m hostile now, wait till you see me tonight.

J: Do you two know each other?

G: Yeah, she’s my fiancé.

J: Well, that would certainly explain the hostility.

P: Your Honor, I object to this witness. Improper foundation. I’m not aware of this person’s qualifications. I’d like to voir dire this witness as to the extent of her expertise

J: Granted. Mr. Trotter, you may proceed.

P: Miss Vito, what’s your current profession?

M: I’m an out of work hairdresser.

P: Out of work hairdresser? Now, in what way does that qualify you as an expert in automobiles?

M: It doesn’t.

P: In what way are you qualified?

M: Well, my father was a mechanic, his father was a mechanic, my mother’s father was a mechanic, my three brothers are mechanics, four uncles on my father’s side are mechanics–

P: Your family is obviously qualified, but have you ever worked as a mechanic?

M: Yeah, in my father’s garage, yeah.

P: As a mechanic? What did you do in your father’s garage?

M: Tune-ups, oil changes, brake relining, engine rebuilds, rebuild some trannies, rear end–

P: Okay, okay. But does being an ex-mechanic necessarily qualify you as being an expert on tire marks?

M: No, thank you, goodbye.

J: Sit down and stay there until you’re told to leave.

G: Your Honor, Miss Vito’s expertise is in general automotive knowledge. It is in this area which her testimony will be applicable. Now, if Mr. Trotter wishes to voir dire the witness, I’m sure he’s going to be more than satisfied.

J: Okay.

M: All right, all right. Now, Miss Vito, being an expert on general automotive knowledge, can you tell me what would the correct ignition timing be on a 1955 Bel-Air Chevrolet with a 327 cubic inch engine and a four-barrel carburetor?

M: It’s a bullshit question.

P: Does that mean that you can’t answer it?

M: It’s a bullshit question, it’s impossible to answer.

P: Impossible because you don’t have the answer.

M: Nobody could answer that question

P: Your honor, I move to disqualify Miss Vito as an expert witness.

J: Can you answer the question?

M: No, it is a trick question.

J: Why is it a trick question?

M: Cause Chevy didn’t make a 327 in ’55. The 327 didn’t come out till ’62, and it wasn’t offered in a Bel-Air with a four-barrel carb ’til ’64. However, in 1964 the correct ignition timing would be four degrees before top dead center.

P: Well, uh, she’s acceptable your honor.

Thus, Mona was established as an expert in the field of general automotives. She did not have an type of specific tire mark expertise, but she had sufficient expertise to be able to assist the jury.  

Silly experts, Gambini started out trying to establish her expertise. Mona was not really cooperating at first. The prosecutor then got involved and conducted a more aggressive voir dire. By the end, even he was satisfied with Mona’s expertise. Eventually, she was accepted as an expert witness.

voir dire of Mona as an expert witness - marisa tomei my cousin vinny
My Cousin Vinny photo from Mubi

Lets look carefully to see if Mona satisfied the rule to qualify as this expert.

(A) Expert Witness Helpful to the Jury

Does her technical or specialized knowledge help the trier of fact (the jury) understand the evidence or to determine a fact in issue?  To answer this question lets look at more of Mona’s testimony:

G: Your Honor, this is a picture taken by my fiancee outside the Sack O’ Suds. Do we agree on this?

P: Yeah.

G: Thank you. I’d like to submit this picture of the tire tracks as evidence.

Judge: Mr. Trotter?

P: No objection, your Honor.

G: Miss Vito, did you take this picture?

M: You know I did.

G: And what is this picture of?

M: You know what it’s of.

G: Miss Vito, it has been argued by me, the defense, that two sets of guys met up at the Sack O’ Suds at the same time, driving identical metallic mint green 1964 Buick Skylark convertibles. Now, can you tell us, by looking at the picture, if the Defense’s case holds water? (pause) Miss Vito, please answer the question. Does the Defense’s case hold water?

M: No, the Defense is wrong!

G: Are you sure?

M: I’m positive.

G: How could you be so sure?

M: Because there is no way that these tire marks were made by a 1964 Buick Skylark. These marks were made by a 1963 Pontiac Tempest.

P: Objection your honor, can we clarify to the court whether the witness is stating fact or opinion?

Judge: This is your opinion?

M: It’s a fact.

G: I find it hard to believe that this kind of information could be ascertained simply by looking at a picture.

M: Would you like me to explain?

G: I would love to hear this.

J: So would I.

M: The car that made these two equal length tire marks had positraction, can’t make those marks without positraction, which is not available on the 1964 Buick Skylark

G: And why not? What is positraction?

M: It’s a limited slip differential which distributes power equally to both the right and left tires. The ’64 Skylark had a regular deferential, which anyone who’s been stuck in the mud in Alabama knows, you step on the gas, one tire spins, the other tire does nothing.

J: That’s right.

G: Is that it?

M: No, there’s more, you see, when the left tire mark goes up on the curb, and the right tire mark stays flat and even, well, the ’64 Skylark had a solid rear axle, so when the left tire would go up on the curb, the right tire would tilt out and ride along its edge, but that didn’t happen here, the tire marks stayed flat and even. This car had an independent rear suspension. Now in the 60’s there were only two other cars made in America that had positraction and independent rear suspension and enough power to make these marks. One was the Corvette, which could never be confused with the Buick Skylark. The other had the same body length, height, width, weight, wheel-base, and wheel-track as the 64 Skylark, and that was the 1963 Pontiac Tempest.

G: And because both cars were made by GM, were both cars available in metallic mint green paint?

M: They were.

G: Thank you Miss Vito, No more questions. Thank you very, very much. You’ve been a lovely, lovely witness.

J: Mr. Trotter, would you like to question Miss Vito? (pause) Mr. Trotter? Mr. Trotter? (Banging gavel.)

P: No further questions.

Mona responded to the prosecutor’s objection that she was testifying to a fact not an opinion. But to quote Mona, it was a “bullshit” objection. Of course, she was testifying about her opinion. She was not at the murder scene, and she did not see which car made the tracks.

However, it was her expert automotive opinion, as an expert witness,  that that the car that made the tracks in the photo was not the car being driven by the two defendants.  Some other car that could have easily been confused with the defendant’s car must have made the tire marks, that was her expert opinion!

Was this testimony helpful to the jury or did it assist them in deciding an important issue in the case? You betcha!

If the car being driven by the accused was not the car that left the marks, then that supports the inference that another car left the marks. If another car left the marks then there had to be another car at the Sac O’ Suds around the same time that both defendants were there. That is definitely helpful information for the jury to have.

(B) Based on Sufficient Facts or Data

Ok, but Rule 702 Requires a little bit more. Did the expert witness, Mona, testify based on sufficient facts or data? In this case, the sufficient facts and data was the photo. It seemed to be of a sufficient quality that she could draw the inferences from it that she did. One would have thought that the prosecutor would have pointed out deficiencies in the photo if any were there. 

Angry Judge Qualify Mona as an Expert: Expert Witness Defined by Marisa Tomei
Holly Crap, She’s Going to Qualify as an Expert!

(C) Product of Reliable Principles and Methods

Did Mona, as an expert witness, depend on reliable principles and methods?

Usually, this point is addressed by scientific theory or laboratory techniques. The question is really asking if the scientific principles and the laboratory techniques are sufficiently reliable to allow accurate conclusions to be drawn.

Well, Mona was not challenged on this issue. She was relying on the laws of mechanical engineering, physics, and the body of automotive knowledge and history that she was aware of. Nobody seemed to be suggesting that she was wrong on the the laws of mechanical engineering. Nor did anyone believe that the laws of physics seized to exist for those brief moments when the tracks in that photo were laid down. [Sorry, I could not help myself with that one.] Also, nobody questioned Mona’s general automotive knowledge.

(D) Reliably Applied Principles and Methods

Finally, did Mona reliably apply the principles and methods to the facts of the case? Was she correct, in other words? Typically, its up to the expert witness herself to explain that their opinion is reasonable and accurate. The expert witness is allowed to explain as best they can the logic and reasonableness of their conclusions.

 Usually, the attorney’s last question is something along the lines of weather their opinion “in this case is based upon a reasonable degree of automotive certainty acceptable in your field?” And the expert witness says, “Yes.” On this last point, this is where the opposing party is likely to call their own expert witness to explain to the jury that everything the first expert said is flawed, inaccurate, or wrong because she did not reliably apply the principles and method to the fact of the case.

However, the prosecutor did not use his expert witness to challenge Mona’s opinion. In fact, the prosecutor’s expert witness agreed with Mona’s opinion and analysis. Remember, Gambini recalled the prosecutor’s expert witness to help establish this last point of Rule 702. The testimony went like this:

G: In that case, your Honor, I’d like to recall George Wilbur.

J: Miss Vito, you may stand down. (To Wilbur “W”) You realize you’re still under oath?

W: Yes, sir.

G: Mr. Wilbur, how’d you like Miss Vito’s testimony?

W: Very impressive.

G: She’s cute too, huh?

W: Very.

J: Mr. Gambini?

G: Sorry, sorry, your Honor. Mr. Wilbur, in your expert opinion, would you say that everything that Miss Vito said on the stand was 100% accurate?

W: I’d have to say that.

G: And is there any way in the world that the vehicle the defendants were driving made those tire tracks? It’s okay, go ahead and say it, they know.

W: Actually, no.

G: Thank you, no more questions.

J: Thank you. You may stand down now, Mr. Wilbur.


Yes, apparently that scene where Gambani calls his girlfriend as an expert witness in the murder trial he was defending was possible because she was called to testify as an expert witness not as an occurrence witness.

Additionally, Mona was properly qualified as an expert in the field of general automotives. And Mona was able to provide competent useful testimony for the jury.

Indeed, I would give up a pinky toe to have an expert witness as effective as Mona was in explaining to the jury a complicated opinion as smoothly and reliably as she did. See also Differences Between Expert and Lay Witness. 

Whala! My Cousin Vinny, Mona Testifies as an Expert Witness
My Cousin Vinny: Ta-Da!
Categorized as Expert

By Arthur McGibbons

Arthur McGibbons has acquired the rights and content to this website. Samuel Partida, Jr. has transferred ownership of this site to Arthur McGibbons.

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