PITTSBURGH — A jury won’t decide Melvin Knight’s guilt when he goes on trial today in the torture slaying of a mentally disabled woman held captive for two days in an apartment by six people she thought were her friends.

The 22-year-old Swissvale man pleaded guilty to first-degree murder in April, showing, legal experts say, he believes his only hope is that the jury will sentence him to life in prison instead of the death penalty for acknowledging what he did.

Duquesne University law professor and death penalty expert Bruce Ledewitz said this type of message from a defendant — that he knows he did something terrible and regrets it — “is crucial in death penalty cases.”

The penalty phase, a trial in itself, is expected to last up to 10 days in Greensburg, where the woman’s torture took place, about 30 miles east of Pittsburgh.

Knight’s attorney, Jeffrey Miller, didn’t return telephone calls seeking comment. Westmoreland County District Attorney John Peck declined to comment.

But Ledewitz and University of Pittsburgh law professor John Burkoff, an expert in criminal defense strategies, said Knight’s strategy means he believes his only hope is for the jury to have more mercy on him than he had on 30-year-old Jennifer Daugherty, described by her family as having the mental capacity of an adolescent.

Daugherty’s body was found wrapped in plastic and stuffed into a garbage can that was wedged under a truck parked in a middle school parking lot in a snowstorm on Feb. 11, 2010. Daugherty’s head was shaved, and her face was painted with nail polish, indignities police determined were among the least she endured.

Police believe Knight and five other people tortured Daugherty after she visited an apartment the others informally shared.

That’s where Angela Marinucci incited the others to beat and abuse Daugherty because Marinucci was jealous that Daugherty also had a sexual relationship with a petty criminal named Ricky Smyrnes.

Marinucci was convicted and sentenced last year to life in prison; she wasn’t eligible for the death penalty because she was only 17 when the crimes occurred. Smyrnes, 25, whose lawyer has said he has “extremely low mental functioning,” is set for trial in October.

Amber Meidinger, 22, who was pregnant with Knight’s child at the time, and another couple accused of having a lesser role in Daugherty’s torture, are awaiting trial but have been cooperating by testifying to the grisly details.

They’ve said Daugherty was tied up with Christmas lights and tinsel, compelled to write a suicide note, then forced to drink a cocktail of human waste, laundry bleach and prescription drugs. Knight stabbed her on Smyrnes’ orders before both men choked her in a tug-of-war using Christmas lights wrapped around her neck.

The 12 jurors must sentence Knight to death if they decide unanimously that the aggravating circumstances of Daugherty’s death outweigh mitigating circumstances in Knight’s favor, namely his contrition and unspecified mental health issues.