A murdered teenager was failed by police and social services after it emerged they knew her killer had carried out an earlier attack, a serious case review has found.
Jamie Reynolds tried to strangle a girl in 2008 and went on to hang 17-year-old Georgia Williams in Telford in 2013.
Georgia's father, himself a detective constable with West Mercia Police, has called for the publication of an "embarrassing" police report.
A number of agencies admitted failures.
West Mercia Police was investigated over its previous dealings with Reynolds.
An inquiry by Devon and Cornwall Police, seen by the BBC, and given to West Mercia in March, looked at how police dealt with Reynolds after he tried to strangle a girl in 2008.
The investigation resulted in misconduct meetings for four officers and a member of police staff.
One of the officers has been promoted, Mr Shaw confirmed, as a serious case review into failings by police and other agencies was published on Wednesday.
He said: "We have to review our procedures and see how that [promotion] came around.
"Had we been in possession of all the information at the time, we may have made a different decision."
Mr Williams said: "We cried when we read this report and we cried even more when we read the Devon & Cornwall report.
"In our eyes it's ten times worse. It will be an embarrassment to the police but it should come out because this is only half the story."
Mr Williams, and his wife Lynnette said they believed Georgia's death could have been prevented if agencies tasked with working with Reynolds had "done their jobs properly".
Responding to the findings of the serious case review they said: "It was so obvious that Reynolds was, if not one already, a murderer in the making."
Reynolds was jailed in December 2013, at the age of 23, after admitting murdering Georgia.
At the time of his sentencing, Stafford Crown Court was told Georgia knew Reynolds but had "made it clear she had no romantic interest in him" and only agreed to go to his house to be a model for his amateur photography.
Chief Constable David Shaw, of West Mercia Police, said: "We could have and should have done better. We let Georgia down."
The serious case review found in the force's investigation of Reynolds' attempt to strangle a 16-year-old girl at his home in 2008, police had treated it as an assault, the girl's injuries were not photographed and neither she nor Reynolds were referred to a forensic medical examiner.
He was given a final warning.
Report highlights missed opportunities to intervene
- In 2008 Reynolds tries to attack a 16-year-old girl by luring her to his house and grabbing her by the throat. He was given a final warning by police
- A doctor assesses he has become a "significant risk to others"
- In 2011 Reynolds is reported to police for reversing his car into a girl who spurned his advances. No link is made to the existing information on him
- In 2013 he lures Georgia Williams to his home on the pretext of helping with a photo shoot. He kills her by hanging her from a length of rope attached to a loft hatch
In 2011, Reynolds was reported to police for reversing his car into that of a girl who had spurned his advances.
The report said no link was made to the 2008 incident, and had the matter been looked into, it would have highlighted Reynolds' developing behaviour.
Nooses and pornography
Reynolds' own stepfather had told the Justice Liaison Service he had discovered the then teenager viewed images of naked women being strangled.
He also told the service Reynolds had photos of girls he knew with nooses drawn around their necks, the review team said.
The service advised Reynolds' stepfather to tell the police himself, but the force failed to act on it, the report said.
The review team stated a "flawed" decision was made by agencies not to tell the girls in the photos about them.
'Life in danger'
One of them, Jadine Dunning, was only shown one of the photographs after Georgia had been murdered.
She waived her right to anonymity and said: "They've put my life in danger there. Not only my life, other young girls' lives and I think that's completely wrong."
The report stated: "Although at least eight agencies... had involvement in the case, at no time did all those agencies meet together and there was no clear and co-ordinated approach to multi-agency working."