Chances were missed to help a teenage girl in the months before she was raped and murdered by a lodger at her home, a report found.
Police and social services have both been criticised over the case of Lucy McHugh, 13, who was stabbed 27 times by Stephen Nicholson, in Southampton.
Concerns Lucy was being abused were not investigated, the report by Southampton Safeguarding Children Partnership said.
Nicholson was jailed for life last year for Lucy’s killing, in July 2018.
During his trial at Winchester Crown Court, the jury heard that the night before she was murdered Lucy had told Nicholson she was pregnant.
The review said that before that however, Lucy’s teachers had flagged concerns she had an older boyfriend who could be sexually exploiting her.
But social workers considered the concerns had “no foundation” because they were given “assurances” by Lucy’s mother.
As a result, the Multi Agency Safeguarding Hub (Mash) did not follow up the concerns and no information was connected with details held by police, the school or social services.
Both children’s social care staff and the police were aware Nicholson had a criminal history.
Lead reviewer Moira Murray, said: “The referrals needed to be treated as one of child protection.
“If this had happened, a strategy discussion could have been convened concerning the risk this man posed to Lucy and her family.
“This did not happen and was a missed opportunity.”
The report added Hampshire Constabulary showed a “lack of professional curiosity” by not further investigating Nicholson’s background when he came to their attention prior to Clare’s death, including when it became known he was tattooing under-age young people.
Southampton City Council’s executive director apologised to Lucy’s family for the “council’s shortcomings”, and said it had made a number of changes and was determined to keep improving its procedures.
Supt Kelly Whiting, district commander for Southampton, said the constabulary had taken action to improve referrals to other agencies and it had now set up a scrutiny panel to oversee such procedures.