A: "Falsus In Uno" is a term used by a trial Judge in the State of New York to describe what a jury can do if they believe that a witness has lied about one fact in the trial. Here's what I mean...
Let's say a witness has testified about her past employment history and goes for a job interview. In her work history she claims she worked for The New York Times as a reporter and also the Boston Globe. She gets hired and does well at her job. However, it later is revealed that she never worked at the New York Times. Nevertheless, she still keeps her job.
However, years later she got into a car accident and claimed she suffered lost income because of her accident. During the lawsuit the attorney for the other driver questioned her and asked her about where she worked in the past. She testified she worked for the New York Times and the Boston Globe, and was even asked how much she earned at each of those jobs. Once the attorney receives a reply from the New York Times human resources department that this woman has never worked there, a credibility dilemma has arisen for the injured woman.
True, she created the problem on her own, but what effect, if any, could it possibly have on her accident case many years later? The short answer is everything. The long answer is everything too. Here's why:
Credibility is the key to any lawsuit. The person who brings the lawsuit is expected to have 'clean hands' and not have done anything wrong. The attorney for the person(s) you've sued will do everything possible to dig around in your background to find inconsistencies and contradictions. Why do they do this? Mainly to impeach your credibility. To show to a jury that if you have lied in the past, why should we believe your story now?
The "Falsus in Uno" charge is an instruction given by the trial judge to the jurors letting them know that if they find that a witness has lied about something, they are entitled to disregard some or all of that witness' testimony. That 'little white lie' that she may have told years earlier to get her reporting job may come back to haunt her in her current car accident case. You might say, "What does her lie, years earlier, have to do with the injuries she suffered and how disabled she is now?"
The answer is everything. The defense will do their best to show that since you lied about something in the past, how can we believe the extent of your injuries now? Even though they may seem unrelated, the woman's credibility is her entire case. If the jury believes her, she will likely get compensated. If they do not believe her, she will likely leave court without any money. Credibility is everything at trial.