'Deeply disturbed' Miles Hughes was just 17 when he stabbed the 15-year-old girl repeatedly with a Stanley knife, before launching the horrific sex attack.
He had pinned the girl down on the ground, grabbed her round the neck and raped her, ignoring her pleas for him to stop in north London's historic Hampstead cemetery.
After fleeing the scene, Hughes - now 18 - called police to say he had murdered a girl in the graveyard
When cops searched Hughes’ bedroom, they found a hand-drawn picture of a clown adorned with a Nazi Swastika and 666 - the number of the Devil.
A second sketch of a person bore the words: "Anger creates Monsters, Hatred gives them reason".
Hughes told police the drawings were a depiction of voices in his head and said they had told him to kill the victim.
Hughes denied attempted murder and rape, but an Old Bailey jury yesterday found him guilty of both charges after 16 hours of deliberations.
Judge John Bevan QC told Hughes he is “bound to receive a substantial sentence” next month, ordering psychiatric assessments of the teenager to judge how much of a danger he poses to the public.
He said the clown drawing and a letter to the victim after he had been arrested “seemed to me to display a lack of real emotion and an absorbing self-interest which I find deeply disturbing.
“I’m bound to say I will take some persuading he is not self-absorbed, jealous, and controlling to a degree that makes him dangerous.”
Hughes was convicted first by the jury of attempted murder, having already admitted wounding with intent by stabbing the girl.
In a police interview, the victim told how he pulled his trousers down, grabbed her neck and raped her.
She said she tried to fight back, but was repeatedly knifed in the neck and chest, leaving her with puncture wounds, lacerations and scratches.
Hughes finally fled when a member of the public shouted "get off", allowing the girl to get help and call for an ambulance.
During the trial, Hughes claimed he had sex with the girl consensually and denied trying to kill her.
"I intended to cause her really serious harm and nothing else," he admitted.
Hughes, of Dynham Road, Camden, will be brought back to court for sentencing on February 24.