False evidence is evidence presented in a legal case that cannot legally be relied upon for any number of reasons, ranging from genuine forgery of evidence to illegal means of procurement that bar the evidence from court even if it is factually valid. This can include spoken testimony, as well as physical evidence. The standards of evidence are designed to exclude false evidence but there have been a number of noted cases involving questionable evidence that led to convictions or acquittals in legal cases.
Inadmissible evidence includes evidence acquired illegally, such as evidence taken during an illegal stop and search, along with evidence that was not properly documented when it was collected. If there are doubts about the chain of custody for evidence, it must also be excluded on the grounds that it could have been falsified or forged. Once evidence is collected, it must be in the control of law enforcement at all times, whether it is in the physical custody of an officer or in a secured lockup area where evidence can be stored. If evidence is left out without adequate supervision at any point, it is compromised, and cannot be used in court.
Some cases of false evidence have involved particularly egregious examples of falsification, forgery, or tainting where law enforcement or prosecutors were directly involved in the cover-up of information about evidence that would have led to its exclusion. Sometimes evidence is excluded on false grounds, and this can cause equal harm to a case. Exonerating or potentially convicting evidence that is kept out of court can have a profound impact on the outcome of the trial.
Both sides in a case have the right to examine physical evidence presented in the courtroom. This examination gives people an opportunity to challenge evidence if they have questions or concerns or suspect that it is false evidence. An inspection may reveal signs of forgery or tampering that could be used to argue that the evidence should be excluded. For instance, if something found at the crime scene was switched out while it was in the custody of law enforcement and the defense can demonstrate that the evidence presented in court is not the real item, that object could be excluded from the trial.
When people testify on the witness stand, they swear to tell the truth. Giving false evidence can expose people to the risk of perjury charges. Falsifications can include outright lies, as will as omissions of information. It is important to answer questions thoroughly, accurately, and completely, and statements such as “I don't know” are appropriate if a witness generally does not know the answer. Witnesses can also ask to have questions repeated or clarified to make sure they understand what is being asked. Witnesses can be cross examined by opposing counsel under the same rules that allow opposing counsel to inspect physical evidence.