What is a fact? Anything coming out of the mouth of a witness is their view (opinion) of the facts. Some things are not able to be contradicted and apparently factual. I assume expert opinions may or may not fall into this category. It’s legendary that some court cases revolve around dueling (hired) expert witnesses so not every expert opinion is actually a fact. It’s simply the expert’s interpretation of the evidence, which they have expert knowledge available to interpret.
IANAL…
In this movie, the expert opinion is that the tracks come from a particular type of car/transmission and that the evidence of the tire tracks bears this out. The prosecution is free to bring out a reasonably qualified expert to produce “alternate truths” about the evidence, should they be able to produce one. Presumably if a contradictory expert with a contradictory explanation of the evidence cannot be found, the jury only hears the one expert opinion. For example, DNA evidence or fingerprint evidence is presented by experts - the defense is free to argue with their own experts explaining why the “opinion” is wrong.
(I recall a recent case where an Ontario lab was called to produce “partial DNA evidence” in a decades-old murder case. The defense’s experts said the science was junk. The fellow was convicted, the appeals court decided more weight be given to the contradictory experts plus other exonerating evidence, and in a second try, he was acquitted. Google “Candace Derksen”)
There are several different kinds of evidence, for example, eyewitness evidence, documentary evidence, etc. When a person is called to the stand to testify, E is generally only allowed to give evidence of things E had direct experience of, and is very rarely allowed to offer opinions beyond those direct experiences.
An expert witness is allowed to give opinions of evidence in the record based on es expertise. So, there was the photograph of the tire tracks. Monalisa’s established expertise made it possible for her to offer her opinion that the tracks could not have been made by X vehicle and must have been made by Y vehicle.
The typical distinction between a “fact” witness and an “opinion” witness is “personal knowledge.” (A “fact” witness testifies about something that he heard, said, or did). An “expert” opinion is one that relies on “scientific, technical, or other specialized knowledge.” At the margins, the lines are fuzzy and somewhat arbitrary.
One area where, I guess, it gets fuzzy is that an expert can testify to “facts” that he relied on that aren’t really personal knowledge (most of the time those “facts” form part of the “specialized knowledge”).
When I tried to watch the video in the link, it shows the bit where Vinny objects to an inadequate expert disclosure, but I don’t think that’s what you’re talking about.
And part of the testimony scene has the prosecutor conferring with his expert about what she is saying (and not looking happy about the answer). And I believe Vinnie then recalls that expert to get him on the record that Monalisa is indeed correct in her conclusions.
Not a lawyer, but it seems to me that she was not an acreddited witness so it would be an opinion. If I switched it up, and had a lay person give a medical diagnoses on the witness stand, instead of a Doctor then it would be an unqualified opinion, regardless if the diagnosis was correct.
But her point was that the Corvette looks very different from a Skylark. It doesn’t matter if the witness isn’t a car person and has no idea what a Corvette is. If the witness had seen the defendants drive up to the store in their Skylark, and then later saw the real robbers drive away in a Corvette, there’s no way they would think they were the same car, because they look so different. Not so if the robbers were driving a Tempest.
The line between fact and opinion is often blurred. Facts don’t have to be based upon personal knowledge. I know that Thomas Jefferson was inaugurated as the Third President of the United States on March 4, 1801, but I didn’t see that.
Facts are generally things that can be proven either true or false. And opinion is basically an inference based upon facts. Expert opinions are allowed in court because those witnesses are especially qualified more so than a layperson to give those types of opinions.
In typical English, though, the difference between fact and opinion exists on a continuum. On one hand whether the car was a Buick Skylark can be proven true or false, depending on the quality of the evidence or it can be an opinion based upon the observation of surrounding facts. Marissa Tomei did the latter legally speaking. When she said “No, that’s a fact!” she was using colloquial English basically saying that her opinion based on the evidence was so powerful that it could be proven true.
Example:
Poster 1: Climate change is caused by man-made activity
Poster 2: That’s your opinion.
Poster 1: No, that’s a fact.
Poster 1 is arguing that based upon all reasonable inferences from facts that the opinion he espouses is so thoroughly beyond reasonable dispute that it can be verifiably proven true, and is thus no longer a mere opinion, but a fact.