Vetting systems at Cambridgeshire police contained "weaknesses" at the time Ian Huntley was being checked, its chief constable has admitted.
Tom Lloyd's Cambridgeshire force gave Huntley the all clear
Tom Lloyd said other checks from the same year would now be investigated.
He apologised for two human errors made during the vetting of Huntley, who was then cleared to work as a school caretaker in Soham.
The Bichard inquiry is examining how Huntley got the job despite a string of sex offence claims against him.
Huntley went on to murder pupils Holly Wells and Jessica Chapman, both 10, in 2002.
On Thursday Mr Lloyd told the inquiry he wanted to know if other checks had also not been done in 2001.
"The reason we are here today is because of the tragic events of August 2002. Nothing can redress what happened to Holly and Jessica.
"As I think of that...it gives me the resolve to make
sure that what I do, and what my colleagues do, will be designed to ensure that what has happened by way of failings never happens again," he said.
Mr Lloyd earlier said he took "full responsibility" for the errors made.
The inquiry heard an internal report published last November had already criticised the force's vetting system.
And Mr Lloyd apologised for two specific errors made in checking Huntley's application for a job at Soham Village College in December 2001.
One member of staff, Stephen Barnes, entered Huntley's date of birth incorrectly on to the Child Access database, he said.
And Police National Computer operator Jacqueline Giddings failed to check the name Huntley, only looking for his alias, Nixon.
Both employees received "words of advice" as punishment but Ms Giddings' "significant error" was more serious because it was a missed chance to link the names Huntley and Nixon, he said.
Mr Lloyd went on to reiterate it was now "more likely than not" that Humberside police was never asked to vet Huntley.
Last week it emerged Cambridgeshire police had admitted it was unlikely an intelligence check request was sent to Humberside, which had handled sex allegations against Huntley.
Before the inquiry, Cambridgeshire had maintained it did fax a request.
But even if it had, Humberside would not have had any records because of flaws in their intelligence handling, the inquiry has already heard.
Mr Lloyd said his force's internal investigation found "shortcomings" in the supervision and management of Cambridgeshire Criminal Records Bureau (CRB). He said those weaknesses had now been removed.
The report's author, Detective Chief Inspector Gary Ingrey, said he found an "apparent complacency" towards child access checks.
But he said he was satisfied no police officers involved in the Huntley checks showed any evidence of misconduct.
The inquiry has been adjourned and will resume on Friday.
Holly Wells' parents, who were at the inquiry on Thursday will appear on ITV1's Our Daughter Holly: a Tonight Special, on Thursday night.