By Steven Shukor
BBC News, London
Stuart Harling lived in a virtual world of violence, serial killers, weapons and sexual perversion, where his wildest desires had free reign.
Harling was portrayed as a loner who lived in a fantasy world
His fantasies feasted on an ample diet of TV crime dramas such as CSI, violent computer games, "insalubrious websites", books and CDs on weapons and crime, the Old Bailey heard.
His grand plan was to steal a car, load it with guns and drive to Equatorial Guinea in west Africa and stage a coup with an army of followers.
He also envisaged carrying out a Columbine-style massacre at his old school where he would get his revenge on the playground bullies who occasionally picked on him.
In interviews with psychiatrists after his arrest, Harling admitted fantasising about breaking into a woman's home and raping her at knife-point.
And he thought death by "suicide-by-cop" would be a "memorable" way to die.
Harling's lawyers argued he suffered from an "abnormality of mind" caused by Asperger's syndrome, which impaired his mental responsibility for the killing.
They said the killing was a sudden reaction to an unexpected situation, such as the screams of his victim, nurse Cheryl Moss, when threatened with Harling's knife.
Far from a spontaneous act, prosecutors said Harling, "influenced and fuelled by the fantasy world in which he lived", had always intended to murder.
"He seemed to want infamy," prosecutor Brian Altman told the Old Bailey.
"He wanted media attention where he would be portrayed as the victim."
Harling had developed an obsessive interest in serial killers after watching a TV documentary on Richard Ramirez, known as the Night Stalker, who killed 13 people in Los Angeles in the early 80s.
Harling was fascinated by serial killer Richard Ramirez
An examination of his computer revealed he searched the Wikipedia website for information about notorious killers such as Dennis Nilson, Jeffrey Dahmer and Colin Ireland.
Several knives, including a sword with a 39-inch blade, a box of condoms, a CD on hand-to-hand knife fighting and a book on forensic science, were recovered from his room.
In a sign that perhaps points to his own desire for notoriety, Harling searched the internet for terms matching "serial killer Essex", "serial killer Romford" and "serial killer Havering".
On the morning after the killing, he scoured news websites, such as the BBC News website and Google news, for information about the police investigation.
"He murdered because he wanted to, for sexual or other gratification or perhaps to see what it was like to kill - like so many of his heroes who he had clearly been researching," said Mr Altman.
"Perhaps he wanted to be the first serial killer in his town."
Before the tragic events of 6 April 2006, there had been few warning signs about what the teenager was capable of.
Harling had an uneventful childhood, growing up in Rainham, east London, where he lived with his parents and younger sister in a three-bedroom terraced house.
"When you look at the defendant's past life and history, his schooling appears to have been perfectly normal," said Mr Altman.
He was a scout leader. He was a black belt in kick boxing and a brown belt in karate by the age of 14 but was not known to get involved in fights.
It is not clear if he was victimised at school but the court heard on one occasion he retaliated against a bully who had picked on him in the classroom.
Harling told psychiatrists he had always felt socially awkward. He mimicked the social manners of other children so as not to be singled out as being different.
'Off the wall'
After leaving school with 10 GCSEs, he signed up to study accountancy at Havering College.
He had little interest in his social life and enjoyed long solitary walks along the Ingrebourne River. These walks turned into "dry-runs" for his murderous plans, the court heard.
One of his few friends, Andrew Holland, told prosecutors Harling was "pretty clever but he could not be bothered with school".
Mr Holland thought Harling was a "bit off the wall in a nice way", prosecutor Brian Altman told the Old Bailey.
"Once he suggested they should get 150 people together and take over a small oil rich African country."
But there were more sinister aspects to Harling's fantasy world.
The tragedy for Mrs Moss is that they were not detected before he decided to act on them.