POLICE lost a Merseyside sex offender who killed a girl he met online, it emerged last night.

Peter Chapman kidnapped, raped and murdered Ashleigh Hall, 17, after tricking her on Facebook.

The 33-year-old was a known sex offender whom police admitted they were unable to trace.

He posed as a teenage boy to trick the teen into meeting him before he killed her and dumped her body in a farmer’s field.

Merseyside Police admitted they were aware Chapman, 33, was no longer living at his registered address in Kirkby.

But they waited eight months before declaring him wanted – and circulating his details nationwide.

A month later, he strangled childcare student Ashleigh and dumped her near a lovers’ lane.

Chapman confessed yesterday – the day his trial was due to begin at Teesside Crown Court.

Prosecutor Graham Reeds, QC, said he used pictures of a boy in his late teens to lure the shy student to him.

She went missing on October 25 last year. She had told her mother she was going to stay with a friend.

Knowing Ashleigh was expecting a teenager, Chapman told her the boy’s father would collect her.

Merseyside Police confirmed he had lived as a high-risk sex offender in Merseyside since 2000.

In March, 2007, he was reassessed and classed as medium risk.

Chapman initially complied with his imposed registration. Officers saw him at home in August, 2008, and spoke to him a month later.

But when they visited him again in January, 2009 – to investigate a traffic offence – he wasn’t home.

Although officers managed to track him down on the phone, they were worried about his address.

They tried to find him on Merseyside before finally making him a wanted man that September.

Chapman, who was living in a hotel and in his car, admitted failing to notify a change of address.