Rainey started his career as a police officer working in Philadelphia, Mississippi. In October 1959, he shot and killed an African American motorist who was getting out of his car on a violation, but he was not prosecuted. He subsequently ran for and was elected to the office of Sheriff in 1963 and has been quoted as positioning himself as "the man who can cope with situations that might arise", a veiled reference to the racial tension in the area at the time.
On June 21 1964, when the three civil rights workers were murdered, Lawrence was visiting his wife at the hospital. It is not clear, and was not proven in the subsequent trial, when he knew about the incident. It was alleged that he learned of the murder early the following morning and deliberately covered it up.
On July 18 1964, Rainey sued NBC, the Lamar Life Broadcasting Company, Southern Television Corporation, and Buford W. Posey for one million dollars for slander due to an interview which Buford gave to NBC during the investigation of the disappearance of the civil rights workers. This lawsuit was unsuccessful.
On January 15 1965, Rainey and seventeen others were arrested and charged in the deaths of the civil rights workers. Because there was at that time no Federal murder statute, they were charged simply of denying their victims their civil rights. In 1967, the case went to trial in Federal court and Rainey was found not guilty (probably on the basis of his alibi), though six others were convicted.
Despite his acquittal, Lawrence was stigmatized by his role in the events. After leaving office in 1968, he was subsequently unable to get reelected or to work in law enforcement. His later careers included periods as auto mechanic and as a security guard in Kentucky and Mississippi. He later came to blame the FBI for preventing him from finding and keeping jobs.