Not to be wrongly tried for a pretend offense is a right afforded to the citizens of the United States by our Constitution. It was listed in the Declaration of Independence as one of the offenses of the tyrannical government our founding fathers rebelled against.
If a private citizen attempted to enlist 12 other citizens to imprison or execute someone; that private citizen has committed a felony punishable by many years in prison.
If a government agent knowingly provides false evidence or testimony to the jury in an attempt to imprison or execute an innocent citizen; no punishable crime has been committed.
Additionally the US Supreme Court has repeatedly extended this almost absolute immunity to civil liabilities; recent examples being Connick v.Thompson and Rehberg v. Paulk.