Determining why two teenage boys raped and murdered 18-year-old Kimberly Proctor is just as important as the crime they committed, says a prominent B.C. forensic psychologist who believes the teens fed on each others deviancy to carry out the horrific act.

Eight court ordered psychiatric exams have deemed the killers, then 16 and 17, psychopathic. A two-week sentencing hearing in Victoria will determine if the pair will be sentenced as adults or as young offenders.

Simon Fraser University Forensic Psychologist Dr Steven Hart says it's important to understand what the young men think about the horrific and heinous crimes they carried out against Proctor.

"What I'd want to know is what does he think about what he did, and why?" Hart, who is not working on the case, told CTV News.

The boys lured the teen to a home and planned her murder as part of a sexual fantasy. The court has heard the teens both had sex with Proctor after she was dead. They also planned to pour a chemical drain cleaner into her body.

Eight court ordered psychiatric exams deemed them psychopathic.

"The grandiosity, the sense of being superior to other people and thinking that you have special abilities," Hart said, describing the traits that would lead to the ruling.

Other killers who have displayed these features are Atif Ahmad Rafay and Sebastian Burns, who schemed to murder Rafay's parents in their Washington State home in 1994. They were both described as arrogant and narcissistic. Rafay is currently serving three consecutive life sentences for the slayings.

Proctor's killers have been assessed as sexually deviant. The 16-year-old talked about sex with corpses and both boys expressed fantasies of group rape.

Psychological and psychiatric reports presented by Crown prosecutors Tuesday described the younger boy as sexually attracted to the psychological and physical suffering of others.

Dr Hart says the scale of violence perpetrated may have escalated because the pair was acting in partnership.

"They end up doing terrible things together, that they might not have even done on their own," he said.

Doctors believe that the teens are untreatable and a high risk to reoffend.

"When we have someone with some psychopathic personality features and who's developing sexual deviance the combination is a very bad thing," Hart says, adding that there is no treatment for either disorder.

In the case of the youngest boy, his father is a convicted murderer. The boy's father is behind bars for the brutal murder of a teen girl under very similar circumstances. In that case, too, the girl was lured, beaten, bound, sexually assaulted, choked and killed.

Hart says there are no genes that would make you kill someone or commit sexual assaults, even if violent behaviour runs in the family.

"It's really that kind of push or the personality problems that you are likely to have that's what seems to be the things people inherit," he said.

Hart says the teens need to be evaluated continually while in custody. Public safety will depend on the boys' treatment in prison and the supervision of them when released.

Crown seeks adult sentence

Prosecutors are arguing that both of the killers should be sentenced as adults in Proctor's murder.

A youth sentence for the teens would mean a minimum jail term of 10 years without parole. That jumps to life with 25 years without parole if they are sentenced as adults.

The details of Proctor's murder were so repulsive and appalling; some officers who worked the case have gone into counselling.

On March 18, 2010, after declining the boys' advances, Proctor was lured to a home of one of the boys where her hands and ankles were duct-taped. They stuffed a sock in her mouth and sexually assaulted her for hours.

A knife was used to mutilate her body and she eventually died. An autopsy revealed she couldn't breathe because of the tape over her mouth.

Her body was placed in a freezer in the garage. The next day the teens carried her body in a duffel bag on a public bus to the Galloping Goose Trail, where they lit her on fire.

With a report from CTV British Columbia's Lisa Rossington