The introduction of evidence is a central component of criminal trials. The prosecution and defense alike must present evidence in order to support their claims. Judges and juries must be convinced by evidence presented in the courtroom, and for the criminal court system to work correctly, all evidence should be pure, real, and untainted.
There have been many instances where accused individuals have been freed due to tainted evidence in the courtroom. Tainted evidence often gives judges and juries "reasonable doubt" about the case, and may be enough to convince them to throw out a conviction. Evidence may be tainted through improper handling, failure to properly seal a crime scene, and intentional tampering. Fingerprints, blood-samples, and bodily-fluid samples are all common pieces of evidence that are highly susceptible to tainting.
There have also been many cases in which individuals have been wrongly convicted on the basis of forged or falsified evidence. Trials involving property or assets often require the presentation of legal documents to prove a case. Forged documents or falsified records are common instances of falsified evidence in the courtroom. Attorneys for both sides often request to examine documents before trial so they can verify the authenticity of the paperwork.
Another issue that sometimes arises during criminal trials is the suppression of evidence. If items or information are withheld from the jury or adjudicator, it is impossible to make a fully informed decision. Defendants, accusers, and even police officers have been accused of suppressing vital evidence to a case. If evidence suppression is uncovered, the case may result in a mistrial or may be dropped altogether.
False testimonies and witness harassment are also evidence-related issues that may occur during criminal proceedings. Witnesses who give false testimony unfairly influence the case and may cause a wrongful conviction or acquittal. Individuals who give false testimony or lie on the witness stand may be prosecuted for perjury and face stiff fines or jail time. Witness harassment occurs when a witness is made to feel threatened if they give a true and accurate account during trial.