A man admits to a 6th killing in north Alabama on Friday, while serving life sentence in Tennessee prison.

Jacob Shaffer, 33, who killed his wife and four others in 2009, now pleads guilty to murdering 50-year-old Sidney Wade Dempsey in Alabama at the start of the killing spree.

"He admitted he killed Sidney Dempsey to see if he had the mettle to go kill his wife and the others," said Jay Town, a Madison County prosecutor. "It was a test. He was just seeing if he could do it." Shaffer reached plea deals in both states to avoid the death penalty in all six killings.

"Jacob Shaffer does not deserve the possibility of life in prison without parole," Town said.

Shaffer admitting to the 6th killing doesn't really change his punishment. However he will still go on trial set for April 29, the maximum sentence he can receive is "life in prison without parole."

Shaffer's estranged wife, Tracie was his primary target and he killed her teenage son, her father and brother and a 16-year-old neighbor in two homes in rural Fayetteville, Tennessee to prevent them from stopping him. He reportedly called the police after the killings and was found at the scene with his 4-year-old-daugther unharmed.

"It was just a jealousy thing if nothing else, that, 'If I can't have you nobody will,'" said Town.