Home Secretary Alan Johnson: ''We have to learn lessons from this''
Lessons must be learned from the "tragic" rape and murder of a 17-year-old girl, the home secretary has said.
Alan Johnson said UK and US authorities were working on ways to flag up when a convicted sex offender goes online.
Peter Chapman, 33, has been jailed for at least 35 years over the killing of Ashleigh Hall in Sedgefield. The known sex offender met her via Facebook.
The Independent Police Complaints Commission is to investigate Merseyside Police's monitoring of Chapman.
Mr Johnson said the government was looking at ways to alert authorities when convicted sex offenders were online.
He said: "What our people in the Child Exploitation and Online Protection (Ceop) agency do is go online themselves to try and lure in these people.
"Whether we can get the technology to flag up when they're [sex offenders] online is something we need to look at."
Liberal Democrat home affairs spokesman Chris Huhne said the Sex Offenders' Register should be upgraded to take account of the use of the internet.
He said: "We do not even require the registration of IP and e-mail addresses of sex offenders, which has now become typical in the United States.
"This would allow police to monitor social networking activity."
CCTV of Chapman confession
He also called for Facebook to fix the "glaring failure" to include on the website the Ceop button, which helps users access advice and report suspicious activity.
Meanwhile the National Association of Probation Officers has cast doubt on whether the authorities have the resources to effectively monitor some 50,000 sexual or violent offenders.
Assistant secretary Harry Fletcher said: "It is virtually impossible for the police to have all but a handful of these people under 24-hour surveillance.
"[Peter Chapman] is clearly dangerous; he uses Facebook to contact a victim so there's lessons there, he uses many aliases and he travels round the country.
"But unless we have literally thousands and thousands of more police officers involved in surveillance, then these things are going to continue to happen."
It's those family conversations, those good lessons about internet safety, that children need to learn all through their growing-up years
Donald Findlater Lucy Faithfull Foundation
Child protection charity, Lucy Faithfull Foundation, stressed the importance of informing young people and their families about safe online behaviour.
"If a young person is going to meet with someone they have only met online, they have to know that there are dangers attached to that," said spokesman Donald Findlater.
"Preferably they don't go and meet; if they are going to, they should be talking to their parents about that fact or... perhaps with friends, so that there are practical, safe circumstances to make that possible.
"It's those family conversations, those good lessons about internet safety, that children need to learn all through their growing-up years - including when they are 17, because that's what didn't go well in this particular case."
Merseyside Police said it had referred itself to the police watchdog "in view of the public interest and concerns raised following the conviction of Peter Chapman and to ensure complete transparency in terms of this particular matter ".
The home secretary had called on the force to respond to questions about the monitoring of Chapman, who was a known sex offender when he used an alias to befriend Ashleigh Hall online.
There was a nine-month gap between Merseyside Police officers realising Chapman had fled his home there and the force issuing a nationwide wanted notice for him in September 2009, one month before the murder near Sedgefield, County Durham.
Chapman had been known as a convicted sex offender in the Merseyside area since 2000.
In 1996, he was jailed for seven years for raping two prostitutes at knifepoint and he had been the subject of several sexual assault investigations since the age of 15.
A Merseyside Police spokesman has said he did not know why the force did not go national earlier than September last year.
Ashleigh's mother, Andrea Hall, has called for offenders like Chapman to be tagged if and when they are released.
But Mr Huhne said tagging all sex offenders was not realistic.
Facebook has said it is "deeply saddened by the tragic death of Ashleigh Hall".
Mother's agony over Ashleigh murder
It urged internet users to employ caution when contacted by people they did not know "as there are unscrupulous people in the world with malevolent agendas".
Ashleigh's college friends have also produced a list, known as Ashleigh's Rules, of guidelines on internet safety.
Ashleigh was raped, suffocated and her body dumped in a field near Sedgefield after agreeing to meet Chapman in October last year.
Earlier that month, she was attracted by a picture of a young, bare-chested man that Chapman - calling himself Peter Cartwright - had posted on Facebook.
Later, 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 - a ruse Chapman invented to persuade her to get into his car.
Chapman picked her up near her home, and then drove her to Thorpe Larches, near Sedgefield, where he attacked and killed her.
Chapman was arrested the following day after a nationwide alert was issued to trace the car he had been using.
He initially made no mention of Ashleigh, but later told a custody officer he had killed someone and led police to the spot where her body was found, almost 24 hours after she left her family home.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.