London: She was a young girl who lacked confidence and simply wanted a boyfriend.

Then Ashleigh Hall clicked on to Peter Chapman's Facebook profile and saw a bare-chested teenager, who was muscular, good looking and — crucially — interested in her.

Tragically for the 17-year-old trainee nursery nurse, the image of her young suitor was bogus. In fact, he was a shaven-headed 33-year-old serial rapist who would lure her to her death and dump her in a ditch.

The appalling case has highlighted the astonishing ease with which potential predators can lure in their victims via social networking sites such as Facebook. Last night, Ashleigh's mother Andrea pleaded: "Parents, ask your kids to tell you who they are talking to online."

As "calculated and wicked" Chapman began a minimum jail term of 35 years for Ashleigh's kidnap, rape and murder, it emerged that despite being a registered sex offender he had vanished off the police "radar" for over a year after his risk level was downgraded.

Costly mistake

Hall, 39, wept as horrific details of her daughter's last few hours were revealed in court. She said later: "Ashleigh wasn't a bad kid. She wasn't naughty. She made one mistake and has paid for it with her life. "Something more should have been done to stop him. He had someone else's photo on his [Facebook] page.

"It's an awful thought that there is a boy out there and this man was using his photo to prey on young girls. It is unimaginable what my family and I have been through."

Chapman had previously been jailed for raping and robbing two prostitutes at knifepoint — including a 17-year-old — but a series of failings allowed him to roam free.

Even on the day he was arrested for the murder, he was on his way to meet yet another "Facebook friend".

He was stopped by police over a suspected arson attack in Newbury, Berkshire, a month earlier.

The case shows how easy it is for teenagers to be targeted for sex or worse by convicted sex offenders who can easily fake their identities online and then arrange to meet them.