Generally speaking, state attorneys (prosecutors) cannot simply bring in any evidence against a criminal defendant for use at a trial, notes Fort Lauderdale criminal defense attorney Moore. The rules of evidence are complicated and vary between each jurisdiction. The Florida rules and the federal rules of evidence have many similarities, although they are not identical by any stretch.
Certain types of evidence is inadmissible in a criminal trial because it is not sufficiently reliable. Polygraph tests, or lie detectors, fit into this category. Even though law enforcement agencies still occasionally use polygraphs when they are investigating serious felonies, the results cannot be used in court. Why is that? For the simple reason that they are not accurate enough. Further, the idea that a machine detects when a person is lying may persuade jurors to give too much weight to its results — even if they are cautioned that the results are not as reliable in reality as they may be in the popular conscience.
Hearsay evidence is also inadmissible in criminal court unless it falls into an exception. Hearsay is perhaps the most famous rule of evidence and determining what is or is not hearsay can be complex. The basic definition is that it is a statement, made outside of court, but offered in the court as evidence of the truth of what the speaker said. For example, suppose that a police officer testified that he heard a woman scream, “Help! I’m being attacked!” The evidence would be hearsay if he testified to it in court and the prosecutor sought to use the statement to demonstrate that a woman was, in fact, being attacked. The statement would not be hearsay, however, if it was offered simply to prove that the police officer was aware there was another person present. Nonetheless, even otherwise admissible statements may be barred if they are too highly prejudicial or not sufficiently relevant to the matter at hand.
The most effective testimony in criminal trials comes from individuals who have personal knowledge of the events to which they are testifying. For instance, an alibi who can credibly testify that his cousin — the defendant — was at their uncle’s house with him, fishing and barbecuing, knows exactly where the defendant was during the time the crime took place because he was there, too. Video evidence can also be highly persuasive. If a man is accused of attacking a woman in Fort Lauderdale around 11:00 p.m., but he locates video footage of the ATM he visited in Fort Lauderdale Beach at 11:13 p.m. or security tapes at the club where he was at midnight, the alibi is strong.