By Tony Hanson

PHILADELPHIA (CBS) – An admitted murderer, Marc Draper, will be back on the witness stand Monday for a life or death hearing. He’s the key witness as the defense fights for a stay of execution for death row inmate Terrance Williams, his co-conspirator in a 1980′s murder.

Williams was convicted of the horrific murder of Amos Norwood in 1984. The victim was beaten and stabbed 20 times. A butcher knife was found embedded in his neck.

Draper helped put Williams on death row and the defense now contends his testimony should save Williams’ life.

Draper has changed his story. Originally, he cooperated with authorities and testified at the trial the motive was robbery.

Draper now alleges he was told to lie to adopt the robbery motive, although he told authorities at the time the murder was actually linked to an abusive homosexual relationship between the 56-year-old Norwood and the teenaged Williams.

The trial prosecutor testified last week Draper is lying, saying he never offered another motive back then. The prosecutor says it is a complete fabrication.

Draper was sentenced to life in prison.