The head teacher who employed Ian Huntley as a caretaker says he would never have done so had he been told of previous claims of rape and burglary.
Howard Gilbert was not told of Huntley's previous burglary charge
Howard Gilbert called for a "rational and balanced system", for schools to find out more about applicants.
Police did not tell him about an unproven charge of burglary, which had stayed on Huntley's records.
Mr Gilbert said he also felt "sick" that allegations of rape and indecent assault had not been passed on to him.
'Must protect children'
On Wednesday Huntley was found guilty by an Old Bailey jury of murdering Soham schoolgirls Holly Wells and Jessica Chapman.
Home Secretary David Blunkett has ordered an inquiry amid criticism of the vetting procedure that allowed Huntley to get a job as a school caretaker.
Mr Gilbert, the head of Soham Village College said so-called "soft information", unproven in court, had to be made available to organisations looking for staff to work near children.
He added: "It's got to change. I understand that there's a civil liberties side as well and we can't set a system up where a malicious allegation could lead to somebody's career being blighted.
"But also we've got to protect children."
Police needed proof "beyond reasonable doubt", he said, while head teachers had to base judgements on "balance of probabilities."
During his interview for the role of caretaker, Huntley had come across as "enthusiastic, keen to please", while showing "lots of energy".
Mr Gilbert said: "Because of our experience with the previous caretaker, I'd like to think we were fairly rigorous anyway as a matter of course, but we particularly heightened the child protection part of the procedure."
Geoff Fisher said Jessica's mother was "amazing"
Huntley was asked what he would do if a pupil developed a crush on him and said he would tell her to stop, or inform a superior if it continued.
The applicant also made it clear he had changed his name to Nixon after a row with his father, but this had not raised concerns, Mr Gilbert said.
A police check did not mention any wrongdoings by Huntley, despite a judge deciding a dropped charge of burglary was serious enough to stay on his records.
Mr Gilbert also said he felt "physically sick" that previous allegations of sex with under-age girls, rape and indecent assault had not been made known.
He said: "The first line in the job description is security. So to have somebody at that level of an allegation of burglary, that is kept on file, would have caused great concern.
"And secondly, we had heightened awareness about the propriety of caretakers in the college and therefore I'm sure we would have acted upon it.
"But we would have been in breach of employment law to have done so."
Mr Gilbert said he could not have acted on any information given, as Huntley had no convictions.
He added: "I'm deeply dismayed hearing that a man with that sort of background was put in a position of trust by me, and was mixing with our children and the staff, and that there was no indication."
Mr Gilbert said: "It's a problem with the situation just now. I think that head teachers are put in invidious positions of being given information that they are then told they couldn't use or they can't use."
Had the information on Huntley become known, Mr Gilbert added: "He would have been sacked. And I hope I'm not just saying that from hindsight.
"We can't have a system where local managers are put in that position and are apparently constrained in what they do.
"That just seems a nonsense. And I hope some good comes out of this and one good could be a review of that to a more rational and a more balanced system."
David Hart, general secretary of the National Association of Head Teachers, called for a "radical overhaul" of the system.
"The current practice of allowing each individual police force to decide what information, beyond a criminal conviction, should be disclosed must be brought to an end.
"It is a lottery that throws up totally different sets of information, depending entirely upon the discretion of the chief constable.
"This must be dealt with as a matter of extreme urgency."
The Department for Education and Skills said the issue was one for the Home Office - which has announced an inquiry.
The head of the school attended by Huntley's victims, Holly and Jessica, said he and his staff remembered them as "two smashing girls".
Geoff Fisher, head of St Andrew's Primary, said Jessica's mother had returned to her job as a support assistant last autumn, after the murders, and was still at the school.
"Sharon has been amazing," said Mr Fisher. "I don't know how she did it, to be honest.
"But she is incredible. Absolutely incredible."
He added: "I think the resilience of people has been quite remarkable.
"The resilience of the children. The way they have tried to put behind them all their anxieties and all their sorrows to make sure the school has gone on."