The man on trial for murdering Tia Sharp wrote to his father from prison claiming that her death was an accident and begging for forgiveness, a court heard today.
Stuart Hazell, 37, wrote to his father Keith from Belmarsh prison in August last year, saying he had made "one mistake and my whole world has collapsed".
The letter, read to jurors at the Old Bailey today, was topped with the words "forgive me" and a sad face.
Hazell, who is accused of murdering Tia, is said by prosecutors to have sexually assaulted the 12-year-old then killed her and put her body in the loft of the home that he shared with her grandmother in south London.
He denies the killing, claiming that Tia died in an accident and he panicked and hid her body.
Hazell wrote: "What happened I will explain in time, but put it this way, it was an accident and I panicked. Stupid I know but for my stupidity I'm looking at 15 to 18 years. I regret it every second of every day.
"I think about ending my life because if I don't someone will, that's definite."
The letter went on: "God I hate myself. I should have gone about this a different way, told the police everything. They're trying to say it was sexual but I promise you it wasn't."
Hazell also asked his father to send money to the prison, saying: "I've got no money, no fags, no hope. It's the Hazell curse and I've only got myself to blame."
He said he had made: "One mistake and my whole world has collapsed. My own fault I know.
"Don't listen to the papers, like everyone else. I will tell you all in time."
The window cleaner wrote that he was "truly, truly sorry", and went on: "May God have mercy on my soul even though I don't deserve it."