Beryl Worthman believes Joey Oliver, the man imprisoned over her son's death, knows more than he has said. (CBC)

The mother of one of the people shot dead in a remote wooded area outside St. John's almost 16 years ago says she is still anxious that a killer is likely on the loose.

Joey Oliver was sentenced Thursday to 15 years in prison for manslaughter in the shooting deaths of Dale Worthman and Kim Lockyer. Because of time served, his sentence was reduced to 11 years.

Beryl Worthman, Dale Worthman's mother, said she wonders if Oliver — who confessed to driving Worthman and Lockyer to the area off Thorburn Road where they were shot one night in August 1993 — has not revealed everything he knows.

"There's no closure because there is no reason," Worthman said after the sentencing hearing in Newfoundland Supreme Court in St. John's, referring to the lack of motive that surfaced during court proceedings this week.

Oliver pleaded guilty Monday to manslaughter, and an agreed statement of facts was also presented to the court.

The court documents show Oliver identified Shannon Murrin as the shooter in the case. Murrin, who is best know for being acquitted in 2000 for the 1994 slaying of B.C. schoolgirl Mindy Tran, has vigorously denied having any part in the Worthman-Lockyer shootings.

Kim Lockyer and Dale Worthman vanished in August 1993 from their Portugal Cove-St. Philip's apartment. Their remains were found in 2006. (CBC)

Oliver told the court that Worthman and Lockyer had been involved in drugs, but he provided nothing to suggest why he lured the pair to a secluded area for what he said would be a beating. He testified that Murrin wanted Worthman, and that he brought Lockyer along because she was at the couple's apartment when he arrived.

"If I could have had a reason why they had to die, I could probably understand it more, but when there is no reason how do you justify [it]? And if there is a third party as they say there is involved, I only hope they get him, and this time it would be first-degree murder, not manslaughter."

Speaking with CBC News on Thursday, Murrin said he believed that Oliver is the killer.

Worthman told reporters she has wondered about that.

"It's a good possibility. Good possibility," she said. "He supplied the gun, the bullets. He had it."

Felt betrayed by Oliver, mother says

In a written victim impact statement presented to the court earlier this week, Worthman said her family felt betrayed by Oliver, saying he would visit them and offer support in the years during which the couple was officially listed as missing.

Their skeletal remains were not found until 2006, shortly after Oliver stepped forward and told the police his account of what happened. He later took RNC officers to the crime scene.

In documents presented to Justice Carl Thompson, the Crown said Oliver's claim about Murrin was uncorroborated.

"We were prepared to accept Mr. Oliver's version of his role, and the corroboration of his role," prosecutor Jim Walsh told reporters.

"The fact that he suggested another person was involved is a matter for further police investigation."

The Royal Newfoundland Constabulary said the Worthman-Lockyer case is still an active investigation. It is not commenting on whether it has any suspects.