Ashleigh's mother said her daughter made a mistake and paid with her life
The family of a teenager who was raped and murdered by a convicted sex offender is questioning how closely police monitored his whereabouts.
Peter Chapman, 33, was jailed on Monday for a minimum of 35 years for the murder of 17-year-old Ashleigh Hall.
Teesside Crown Court heard he posed as a teenage boy on Facebook and met her.
It emerged police had lost contact with Chapman in the months before the crime. Ashleigh's mother, Andrea Hall, said people like Chapman "should be tagged".
Speaking outside court, she said the authorities should have done more to monitor Chapman's whereabouts after his release from prison.
Mrs Hall said: "Them sort of people shouldn't be allowed out into society anyway. I blame them (the authorities) for letting them out.
"He should not have been let out whatsoever and for the people that are supposed to keep an eye on them, they should keep an eye on these sort of people."
Her comments came after it emerged that, following his release from prison, the sex offender was able to move around the country, seemingly free from monitoring.
CCTV of Chapman confession
Merseyside Police said there was a nine-month gap between officers realising the sex offender had fled his home and them issuing a nationwide wanted notice for him in September 2009, one month before the murder.
Chapman at first denied the charges, but later changed his plea to guilty.
On sentencing, Judge Fox said Chapman was, and had been for a "considerable time", a "very great" danger to young women.
"For what it is worth, I cannot foresee your release," he said.
He said Chapman had carried out a "significant degree" of planning and pre-meditation in snaring Ashleigh.
Judge Fox added: "This was an evil scheme very carefully brought, and with considerable detail to trap your victim."
Ashleigh was suffocated and dumped in a farmer's field near Sedgefield after agreeing to meet Chapman.
In October last year, she was attracted by a picture of a young, bare-chested man that Chapman - calling himself Peter Cartwright - had posted on the website.
Later that month, she told her mother she was going to stay with a friend. Text messages showed she thought she was being picked up by "Peter Cartwright's" father.
Since the age of 15, Chapman had been the subject of several sexual assault investigations.
In 1996, he was jailed for seven years for raping two prostitutes at knifepoint.
Chapman had been known as a convicted sex offender in the Merseyside area since 2000.
A statement from Merseyside Police confirmed the nine-month gap between officers realising Chapman had fled his home there and the force issuing a nationwide wanted notice for him.
A Merseyside Police spokesman said he did not know why the force did not go national earlier.
He said: "Merseyside Police continually reviews its policies and processes around the management of sex offenders and to strengthen work with our partner agencies.
"We have also driven locally the national programme (Think You Know) concerning safety on the internet, which aims to keep young people safe while using the internet."
Mrs Hall also warned parents to find out who their children were talking to on the internet.
She said: "Just put the message out that please, parents whose kids are on Facebook, please ask them to tell you who they're talking to. You just don't know who is behind that photo."
Facebook issued a statement after Chapman was sentenced saying it urged people not to meet anyone they had been contacted by online unless they knew who they were, "as there are unscrupulous people in the world with malevolent agendas".
It said there were a variety of measures people could use to protect themselves from unwanted contact and that Facebook strongly encouraged their use.
'Calculated and wicked'
Prosecutor Graham Reeds QC said: "Having invented 19-year-old Peter to make contact with girls, he now decided to invent Peter's dad in order to persuade Ashleigh that it was safe to get into his car.
"The plan he devised was calculated and wicked and it worked."
Mr Reeds said Chapman picked her up near her home, and then drove her to Thorpe Larches, near Sedgefield, where he attacked her.
"After the rape, her arms were bound up again and further tape was put over her face, suffocating her to death," he said.
Her body was dumped in a gully up against a fence by Old Stockton Road.
Chapman was arrested the following day after a nationwide alert was issued to trace the car he had been using.
During initial interviews, he told police they could "crush his car" and made no mention of Ashleigh, but later he lost his nerve and told a stunned custody officer: "I killed someone last night."
He led them to the spot where her body was found, almost 24 hours after she left the family home.
Durham Police have admitted that, had he remained silent, the car would probably have been crushed and valuable evidence lost.
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