Chicago ? A man who has been behind bars more than 50 years in a sensational Chicago murder case in which “Catch me before I kill more” was left scrawled on a bathroom mirror asked a clemency board to free him Thursday, claiming he was railroaded.

William Heirens, 73, was not at the hearing before the Illinois Prisoner Review Board, but a pair of Northwestern University law professors who have worked to free wrongly imprisoned inmates argued on his behalf.

William Heirens, who has served more than 50 years in prison for three notorious 1946 killings, discusses his case in the yard at Dixon Correctional Center in Dixon, Ill. Heirens, photographed Monday, is arguing for clemency.

Heirens, who is believed to the longest-serving prisoner in Illinois, has said he gave a false confession under duress from police and prosecutors who were under intense pressure to solve the notorious 1946 killings of a little girl and two women.

He has claimed he was given a spinal tap without anesthetic, injected with truth serum, subjected to round-the-clock police interrogation and isolated from his parents and his lawyer.

Steven Drizin of the Children and Family Justice Center at Northwestern said Heirens’ case has “all the earmarks of a wrongful conviction.” He asked the 13-member board to “right wrongs which the courts have failed to right.”

Heirens’ supporters have said he is a diabetic and is no threat to society.

Colin Simpson testified on behalf of the Cook County prosecutor’s office, saying nothing has changed in the last 56 years.

William Heirens peers out of his cell in the Cook County Jail in Chicago in this Sept. 5, 1946, file photo. He was sentenced to three consecutive life terms for the murder of a little girl and two women. Supporters of Heirens, who was 17 at the time, say he was tortured and railroaded into confessing.

“William Heirens was guilty of these murders in 1946, and he is just as guilty of these murders today,” Simpson said.

The board will make a recommendation to Gov. George Ryan, who will decide whether to free Heirens. It was not known when the board might make a decision.

Heirens was a 17-year-old student at University of Chicago when he was arrested in the slayings of a 6-year-old girl, whose remains were found scattered in the Chicago sewers, and two women. Heirens was convicted and sentenced to three consecutive life terms.

The message “For heaven’s sake, catch me before I kill more. I cannot control myself” was found scrawled in lipstick on the mirror in one of the women’s home.

Then-Mayor Edward Kelly called the little girl’s slaying “even too horrible for a maniac.”