A convicted killer who died behind bars is considered a person of interest in the mysterious disappearance of a young B.C. mother more than four years ago, CTV News has learned.

Abbotsford resident Candace Shpeley vanished without a trace in March 2007 at the age of 23. The mother-of-three's disappearance was deemed suspicious by homicide police.

Nine months later, 44-year-old Darryl Karl Cole, a man Shpeley's parents say had spent time with their daughter, pummelled a man to death with a baseball bat.

Police now confirm Cole is a person of interest in Shpeley's case.

"He was in her company days before, if not hours before she disappeared," said Sgt. Jennifer Pound of the Integrated Homicide Investigation Team.

Police identified several persons of interest in the investigation, she added.

Pound said Cole's status as a person of interest was never changed, but he was found dead in his jail cell at the Kent Institution over the summer.

Cole was serving a 13-and-a-half-year sentence for manslaughter at the federal maximum security prison when he died. Officials say foul play was not suspected.

There have been developments in Shpeley's case since she went missing. She was last seen by her brother when they met for lunch at an A&W in Chilliwack on March 31, 2007.

Nine days later her 1995 teal-green Pontiac Grand Am was found abandoned in southeast Vancouver. On Thursday, a few months shy of the fifth anniversary of Shpeley's disappearance, her car was released back to her parents.

Shpeley's father Barry said he's still hoping someone will come forward with a new lead, so police can finally crack the case and deliver closure to his family.

"It's a little hard some days. You always think about her. My wife thinks about her constantly," he said.

"It would be nice to be able to say, ‘OK, this is what happened.' Or, ‘We found Candace and she's gonna come home.' Or at least, ‘We know that she's OK,'" he said.

A number of sightings were reported in Chilliwack in 2009, but none was ever confirmed.

Shpeley's son has been in the care of the boy's father since her disappearance, while her two daughters have been living with their grandparents.

"They were young when their mother went missing," Barry Shpeley said. "At first Mommy was just missing, and then now it's not really brought up a lot. The kids go to school in their normal lives. Granddad of course spoils them."

Police ask anyone with additional information in the case, particularly those who were named as persons of interest, to come forward.