Melvin Knight, 23, had contacted prosecutors to say he would testify against Ricky Smyrnes, the accused ringleader in the slaying of Jennifer Daugherty, the Pittsburgh Tribune-Review reported.
However, Knight lawyer Jeffrey Miller intervened.
"Melvin won't be testifying," Miller said.
Smyrnes, 26, is accused of ordering five other people to capture and torture Daugherty for 36 hours, which ended with her being fatally stabbed. The group allegedly beat Daugherty, 30 with a towel rack, forced her to drink cleaning detergents mixed with bodily excretions, and tied her with Christmas lights and garland.
Daugherty's body was found in a trash can in the Greensburg Salem Middle School parking lot Feb. 11, 2010.
Knight pleaded guilty to first-degree murder and was sentenced to death in August.
Also charged in the case are Amber Meidinger, 22, Angela Marinucci, 20, Peggy Miller, 30, and Robert Masters, 39.
Smyrnes' trial began Monday in a Westmoreland County courtroom.