HONOLULU -- Trial began Monday for a 31-year-old murder mystery that involves a key witness who has confessed to the slaying.

Maryann Bray has already served three decades in prison. She claims her husband, William Acker, framed her.

Bray wanted the trial, hoping to prove she was a pawn in her husband's schemes.

"His plan was to use Maryann as bait. She would attract men and William would rob them," defense attorney Keith Shigetomi said.

The couple's second robbery in Hawaii, of Larry Hasker, 20, led to Hasker being executed near Hanauma Bay. Hasker's sister described finding their apartment ransacked while the victim was missing.

"I knew that there was something terribly wrong," Hasker's sister, Kimberly Hasker Alamalach, said.

The prosecution's case will again rely on Acker's testimony.

"He's going to tell you that Maryann shot and killed Lawrence Hasker," Deputy Prosecutor Landon Murata said.

As an inmate in California, Acker testified against some of his cellmates and prison officials took him underground. He now lives under a false name in an unnamed federal facility.

Bray and Acker were convicted together of another fatal robbery in California. Acker later claimed he was the killer. It is not clear what he will say at retrial, especially since he is protected by an immunity deal in Hawaii.

"He has never and will never be prosecuted for shooting Hasker in the back of the head," Shigetomi said.

If Bray is acquitted, she is expected to be released on parole.