Getting Mark Bridger to crack and finally reveal what he did to April Jones could take years, a leading criminal psychologist has said.
Mystery still surrounds the schoolgirl's final moments and the lack of a body or her remains has also cruelly denied her devastated family even the chance to give her a funeral.
Paedophile and former abattoir worker Bridger has continued to play a sadistic game of cat and mouse with police and April's parents since his arrest in October last year.
He has rigidly tried to stick to his fanciful story that he "accidentally" killed cerebral palsy sufferer April - and could not remember what he did with her.
Under repeated questioning - both from detectives and prosecutor Elwen Evans - glaring contradictions started to emerge in Bridger's version of events.
But Nottingham Trent University senior psychology lecturer Serena Simmons said that unpicking the complex web of lies spun by the calculating child killer will be far from easy for prison psychiatrists.
She said: "He clearly is deluded and has a distorted view of the world. He certainly displays this mentality of 'if I keep stalling then eventually things will blow over'. But that is far from the case.
"The reason why killers often refuse to admit the extent of their crimes and their motivation can vary tremendously.
"But he definitely knows what he has done to April Jones and how she came to her death.
"If you question a person repeatedly, especially one who is trying to hide something, then the truth will usually emerge.
"The cracks in his story have already started to show during his trial. He will face more questions while in prison from his psychiatrist.
"Whether he chooses to engage with that process is a different matter, but I fear finding out the full extent of what he did could take a very long time."
Miss Simmons, whose latest research has seen her interview serial killers in the UK and USA, said one of the challenges health professionals encounter in dealing with violent offenders is their manipulative nature.
"Often offenders like Bridger will display a high level of Emotional Intelligence (EI). This is different from someone's IQ and how intelligent they are.
"EI is about an individual's ability to identify, assess, and control the emotions of oneself or others."
Bridger's cunning nature was all too evident during his trial - which saw him cry crocodile tears on several occasions.
"Violent offenders often have a very long back story that you need to unpick before you can attempt to try and get the truth," said Miss Simmons.
"That's not to excuse their actions, but getting a detailed insight into their circumstances and background can be key in finding out any unanswered questions.
"No two people are the same, but there are general characteristics or events that can play a part in shaping someone like Bridger.
"It's quite common for serial killers or violent offenders to have suffered some form of childhood trauma or come from a dysfunctional family. I don't know enough about Bridger's background to say whether that is the case or not.
"However, in hindsight there are some traits he has displayed which may be indicative of concerning behaviour.
"For example, his short tenure as a lifeguard may have aided his sexual fixation with children.
"It is quite common for paedophiles to take 'normal' jobs where they can have access to children.
"While there is no evidence of any abuse carried out by him at this stage of his life, the job may have played a role in his fantasies."
Miss Simmons said the most telling and obvious warning sign was Bridger's disturbing child pornography collection.
The 46-year-old had tried to explain away the sickening images that some were for research purposes, while he kept other photographs as supposed "proof" for a complaint to the website's owners he said he was going to make.
"Often paedophiles will try to justify their actions, or in his case be in complete denial about the reasons why he was accessing child pornography," Miss Simmons added.
"But there is a strong link between the people who access this kind of material and them carrying out sexual abuse.
"Everyone has fantasies, but those who access child porn will often get spurred on by the fact they cannot act out these fantasies - at least to begin with.
"In fact, the evidence I have seen shows that Bridger is a complete fantasist who is far removed from reality.
"The lies he told about being in the army and the supposed death of his parents highlights this.
"And moving into Machynlleth may certainly have aided him initially in controlling the information that people know about him and telling them things he thinks they want to hear.
"He seems to have an explanation for everything."
But Miss Simmons said while the warning signs of Bridger's behaviour have only come to the fore in light of April's murder she does not know whether his murderous intent could have ever been predicted.
"It's a really difficult question to answer," she added. "The trouble is with people like Bridger is that outwardly they appear like a normal member of society - despite what may go on behind closed doors.
"But on the face of things, it does appear to be quite an opportunistic killing, despite how highly organised his actions afterwards were.
"My own personal opinion though, is that he is not a psychopath - labelling him so almost excuses or diminishes his actions. I'm very confident he knew full well what he was doing was wrong."
Miss Simmons - who is helping push the boundaries in the field of criminal profiling - said while pulling apart Bridger's warped mind may help solve other crimes in the future it was important people did not forget April.
"It's quite often the case that people who commit serious crimes like Bridger are remembered instead of their victims," she noted.
"Many people have heard of Fred or Rosemary West, but few can name who their victims were.
"It's important for people to remember April - and that she was someone's daughter as well as sister.
"As much of my work does see me deal with the darker side of humanity, I also look into the amazing things that people do too.
"The response that the local community and further afield gave in the wake of April's disappearance and death has indeed been amazing.
"It has hit a nerve with people everywhere, because there is that sense of 'if it was my child'.
"I'm not being glib about what was a terrible and horrific killing, but the level of support people have displayed to April's family proves that the human spirit cannot be completely beaten.
"You just hope that they will be able to take some small comfort in that."