Soham killer Ian Huntley was officially "eliminated" by police as a suspect in the double murder just six days into the probe, a report has revealed.
Police accepted Huntley's false alibi
Officers leading the search for missing schoolgirls Holly Wells and Jessica Chapman accepted a false alibi given by Huntley's then girlfriend, Maxine Carr.
The report was by the Met's Det Supt David Begg at the time of the murders.
A spokeswoman from Cambs police said: "Huntley's alibi was deemed to be acceptable at the time."
"It was later found to be suspicious," she told the BBC news website.
When Huntley re-emerged as a suspect police did not have enough resources to mount a surveillance operation, the report revealed.
Extracts from it were obtained by The Times newspaper under the Freedom of Information Act and published on Monday.
A spokeswoman for the force said it had "taken on board" all the criticisms contained within Mr Begg's report.
She added that the force's crime investigations structure had been overhauled and that senior detectives were now on call 24 hours a day.
Huntley, 31, was jailed for life for the Soham murders at the Old Bailey in December 2003.