The police force monitoring serial sex attacker Peter Chapman before he fled to kidnap, rape and murder Ashleigh Hall has referred itself to the Independent Police Complaints Commission, it said today.
Merseyside Police were meant to be keeping tabs on Chapman.
But after realising he had vanished from his Kirkby home early last year, they left it nine months before issuing a national wanted alert.
Today, a spokesman said: "Merseyside Police can confirm that an internal review was carried out following the arrest of Peter Chapman in October last year.
"Following the review, a number of procedural improvements were identified and subsequently implemented.
"However, 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 force has referred it to the Independent Police Complaints Commission."
Chapman, sentenced to a minimum of 35 years in jail, was last seen by police at his home on August 29, 2008.
An officer spoke to him on the telephone on September 24 that year about a forklift truck course he was doing.
Merseyside Police said that, up to this point, he "had remained fully compliant with his registration requirements" - forced on him by being on the sex offenders register.
Police visited his home on January 6, 2009 to discuss a traffic matter but he was not in.
Different officers were supposed to visit him a month later in line with his sex parole checks but again he was not in.
The force maintains that officers then worked to establish his whereabouts locally.
But it was not until September last year - just a month before he murdered Ashleigh - that the police issued a nationwide wanted alert.
The force referred its handling and review of the Chapman case to the IPCC after Home Secretary Alan Johnson demanded answers.
The minister called on the police to "respond" and said lessons "needed to be learned" following Ashleigh's murder.
Today, Ashleigh's mother, Andrea Hall, branded the 33-year-old murderer inhuman and called for closer monitoring of sex offenders.
And Mrs Hall, 39, appearing on ITV's This Morning, said the authorities should make public where sex offenders live.
She said: "He took my daughter.
"He shouldn't be allowed human rights; he's not human, is he?
"How is he human?
"He murdered my daughter.
"She was 17 and he knew exactly what he was doing and there was no remorse whatsoever.
"He had it planned... and she was such a lovely girl and that's probably why he targeted her."
Mrs Hall added that she would never let her remaining three daughters, aged between one and six, use social networking website