Perjury is the term used when an individual testifies under oath in a court proceeding to the veracity of the testimony and knows at that time that some or all of it is false. The official charge for this is perjury by false affadavit. These two facets of perjury (testimony under oath and knowingly lying at the time of the oath) must be shown for charges to be filed.
Who Prosecutes Perjury?
When perjury charges are filed, the government is responsible for prosecuting. This usually means the U.S. Attorney, district attorney or city attorney will be in charge. It depends on where the original case that elicited the perjury was tried. The perjury case will be prosecuted in the same court of law. Perjury is rarely tried, but is often used as a threat during criminal trials. Civil lawsuit perjury is even more rare. It is difficult to prove that an individual is lying instead of testifying in an honest manner, but not remembering accurately.
Assigning the Case
The prosecuter in a perjury trial will be representing the people in her district, city or country. This is why the case will be referred to in all legal documents as "the people vs. (defendent's name)". She will be assigned the case by her superior. This may be the district attorney of a county or possibly even the attorney general of the United States.
When Perjury is Prosecuted
The prosecutor of the individual charged with perjury will not file against a participant in court proceedings who lies about nonmaterial issues, such as age. Prosecution of perjury by affidavit is reserved for when the false testimony can affect the outcome of the trial. This does not mean the information actually influences the outcome; only that it could change the outcome. The "people" (prosecutors) do not need to prove that the defendant knew the false testimony would affect the proceedings.
When Perjury is not Prosecuted
The attorney representing the prosecution will not charge a defendant with perjury if there is only one witness to the lie. There needs to be another testimony or some additional evidence for them to consider prosecuting. He will not take the time and incur the cost to bring charges if a witness believes their testimony was true though later found to be false. In addition, if the attorney believes that the outcome would have been the same without the perjury, he will probably not file charges.
Prosecutors of perjury have discretion on whether to file charges. They are influenced by many things, including trial outcome, political aspirations (many district attorneys run for office), office policies and the ideals of the attorney. However, perjury can be a significant offense, especially when an innocent defendant is found guilty. Though it is not always prosecuted, anyone who lies on the stand is running the risk of becoming a defendant in a new trial.