The body of missing murder victim Lisa Dorrian was secretly buried by a father and son.
That is now the major line of inquiry for detectives and why they believe that 14 years after her disappearance, the killer and his accomplice have not given each other up.
Lisa (25) was last seen at a caravan on a site at Ballyhalbert, Co Down, in February 2005 - her anniversary occurs on Wednesday.
Touching on the killer and his colleague's close "bond", the top cop leading the murder inquiry, Detective Superintendent Jason Murphy, said: "I firmly believe that the answers to Lisa's disappearance lie with a small number of people.
"They may believe that they are bound by a common bond and have maintained their silence as a result. That silence will be a heavy and lifelong burden. We can help to unlock that burden, but we cannot do so whilst they remain silent."
Security sources told Sunday Life that they believe how after the Bangor shop worker was murdered her panicked killer, who did not drive and did not have access to a car, contacted his father to help dispose of her body.
This individual, a member of the Red Hand Commando terror gang, travelled from his Co Antrim home to the caravan site at Ballyhalbert in north Down where she was last seen alive.
The father and son are understood to have placed Lisa's body in the boot of his vehicle and secretly buried her nearby. One theory is that she may have been disappeared on land at the rear of the caravan park that was being developed for new houses - the foundations were being dug at the time.
The killer and his accomplice were later able to remove all forensic traces from the car because the initial police investigation centred on a group of criminals who Lisa was in debt to as suspects.
A security insider with detailed knowledge of the case, said: "Lisa's murder was not pre-planned, and her disappearance was hurried.
"The major line of inquiry is that she was killed by 'A', and then realising what he had did he summoned his father 'B' to help hide her body."
PSNI insiders suspect the killer and his colleague were able to remove DNA traces from the car used to transport Lisa's body because the murder inquiry initially focused on a crime gang to which she was linked.
Members of this group, her ex-boyfriend Stevie Thompson (40), Marty Peacock (35) and Mark Smyth (36), have since been ruled out of police inquiries.
Sunday Life can also reveal that Red Hand Commando leaders have accepted that one of its veteran members helped his killer son bury Lisa's body.
Despite this the terror gang - which is petitioning the government to be decriminalised - is refusing to put pressure on him to reveal where her body is hidden.
Cops investigating Lisa's killing and secret burial have so far questioned more than 400 people, taken 1,100 statements, arrested 10 individuals, carried out 306 searches and forensically examined 371 items.
DS Murphy is convinced she was murdered by someone she knew, saying: "They hold the key to the Dorrian family being able to finally put Lisa to rest. I do not believe that Lisa was killed by a stranger, and that leads me to the very solemn conclusion that Lisa was killed by someone that she knew and trusted."
Vowing to continue attempts to recover her body, DS Murphy added: "We have not given up on our pursuit of justice. We have not given up on our search for Lisa's body.
"Those who choose to withhold what they know should expect us to rigorously investigate them."
In the hours before Lisa disappeared she was partying in a Ballyhalbert caravan, which was closed for the winter with few people on site.
The last person to see Lisa alive, teenager Mark Lovett, told police how he and Lisa fled the caravan when they heard noises and saw flashing lights outside. In a second anonymous account given to BBC Spotlight in 2005, the then 17-year-old explained how they lost each other in the dark at 5am.
Lovett said he searched for Lisa and rang her mobile, which was answered by her ex-boyfriend Stevie Thompson, who is not a police suspect. Thompson later told this newspaper he had bought the phone for Lisa, which she had given back to him after they ended their relationship a few days before her disappearance.
Anyone with information about the murder of Lisa Dorrian should contact police on the non-emergency 101 number or the Crimestoppers charity on 0800 555 111.