A police report that spotted a pattern of sex allegations against Ian Huntley was deleted from records in July 2000, the Bichard Inquiry has heard.
Huntley was hired despite prior accusations against him
The report, submitted by Pc Michael Harding in July 1999, suggested Huntley could be a "serial sex attacker".
It was the only time an intelligence report had been drafted on Huntley, inquiry counsel James Eadie said.
The inquiry, lasting five weeks, aims to learn why records of sex allegations against Huntley were deleted.
In the report, Pc Harding said Huntley seemed to choose women who would not make ideal witnesses or complainants.
He said: "It is quite clear that Huntley is a serial sex attacker and is at liberty to continue his activities."
The report was submitted to the divisional intelligence bureau but, the inquiry heard, must have been deleted during a "weeding" process of the records system by civilian staff in July 2000.
Allegations not revealed by checks
Four involving rape
One indecent assault on an 11-year-old
Sex with underage girls
Non-payment of a fine
School caretaker Huntley murdered 10-year-olds Jessica Chapman and Holly Wells in Soham, Cambs, in August 2002.
The probe, sitting in central London, earlier heard how vetting errors and who was responsible for them would be the focus of investigations into how Huntley was employed by Soham College.
The inquiry will specifically look at how allegations of rape, indecent assault on an 11-year-old girl and sex with underage girls were not shared between Humberside and Cambridgeshire forces.
In his opening statement, Mr Eadie said Soham Village College, in Cambridgeshire, had asked for police checks to be undertaken before employing Huntley.
Counsel for inquiry, James Eadie: Hindsight is a wonderful thing
Those checks had revealed no information about the allegations made in and around Huntley's home town of Grimsby, to Humberside Police.
Mr Eadie told the inquiry that when the checks were carried out, in December 2001, two matters had been recorded against Huntley on the child protection register.
One was the allegation of indecent assault on an 11-year-old girl and there was another allegation of unlawful sexual intercourse with a 13-year-old girl.
But the child protection database would not have been searched at the time of the police checks, Mr Eadie added.
Earlier, Mr Eadie said Humberside's child protection database was described by the force itself as "ineffective as a source of information" and "almost
He also said Humberside Police had failed to update Police National Computer records to include Huntley's alias surname of Nixon and so the response to the check in December 2001 would have been "no trace".
Mr Eadie told the inquiry the second main focus of the probe would be on how the systems of checking and vetting could be improved for the future.
He said the inquiry would consider how police records are dealt with, whether the systems by which they are created and stored are effective and whether the systems and the way the information is used strike an appropriate balance.
Huntley was only charged in relation to one of four allegations of rape but the matter never reached court on the advice of the Crown Prosecution Service.
Mr Eadie said Humberside Police had acted differently from many forces in entering details on the PNC at the point of
charge rather than arrest.
He said: "There was a relatively high barrier to information finding its way
onto the PNC."
Records, including Huntley's, were automatically deleted after three years but still retained on magnetic tapes and CDs.
Mr Eadie said: "It was possible on many occasions for an officer to mark a
record 'retain' and keep it on the CIS database."