To turn state's evidence is when an accused or convicted criminal testifies as a witness for the state against his associates or accomplices. Turning state's evidence is occasionally a result of a change of heart or feelings of guilt, but more often is done in response to a generous offer from the prosecution, such as a reduced sentence or a favorable location for serving time. In particularly high-profile or dangerous cases such as organized crime trials including other federal crimes trials, the witness may be offered immunity from prosecution even if he has committed serious crimes himself, up to and including murder. The state may also offer the witness a place in the witness protection program, giving them a new identity so they need not fear retaliation from their former accomplices.
In the United Kingdom, the term is to turn Queen's or King's Evidence, both of which still mean the same thing.
| Witness | Testified against | Charge(s) | Received for testimony |
|---|---|---|---|
| Salvatore "Sammy The Bull" Gravano, mob hit man | John Gotti | racketeering | |
| Frank "Curly" Lino of the Bonanno crime family | Ron Filocomo | murder of Sonny Black Napolitano | ? |
| "Easy Eddie" O'Hare, mobster | Al Capone | tax evasion | According to some sources, his son Butch's admission to the U.S. Naval Academy in Annapolis |
| Harry Orchard, mass murderer | William "Big Bill" Haywood | assassination of former governor of Idaho Frank Steunenberg | ? |
| Jimmy Leibrant, accessory to murder | Karla Faye Tucker | murder of Jerry Lynn Dean | full immunity |
| James Jordan, Klansman and accessory to murder | 18 other Klansmen including Neshoba County deputy Cecil Price | murder of three civil rights workers | full immunity, $3500 and help in relocating himself and his family |
| Christie's auction house | Sotheby's | commission rate-fixing | protection from criminal prosecution (for the business—however the former chairmen of both companies were indicted) |
| Linda Kasabian, driver of the getaway car in the Tate/LaBianca murders | Charles Manson and other members of the Manson Family | multiple murders | immunity from prosecution |
| James "Dick" Liddil, bank robber, murderer and member of the James-Younger gang | Jesse James | robbery, murder | immunity from prosecution |
| Daniel Tucker Bassham, member of the James-Younger gang | William "Whiskey Head" Ryan, member of the James-Younger gang | robbery, murder | 10-yr sentence commuted, released from Missouri State Penitentiary |
| Wayne DuMond, rapist | various acquaintances | murder | pardoned by Gov. Mike Huckabee |
| John Dean | Richard Nixon and others | Watergate | very light sentence, "jail" time served in a safe house at Fort Holabird |
| Robert Rozier, murderer and cult member | Hulon Mitchell, Jr. (Yahweh ben Yahweh), cult leader | murder, racketeering | reduced sentence |
| David Greenglass, spy, passed information about the Manhattan Project to... | ...Julius and Ethel Rosenberg | treason, spying | immunity for his wife, who served as his courier |
| Henry Hill, mobster | Paul Vario and Jimmy Burke | racketeering charges | immunity from prosecution and witness protection for Hill and his family |
| Abe "Kid Twist" Reles, Mafia hit man | Louis "Lepke" Buchalter, members of Murder, Inc. | murder | no death penalty |
| William Hare, the West Port murders in Edinburgh, Scotland | William Burke | murder | immunity from prosecution |
| Joseph Massino, Bonanno crime boss | no death penalty |