A council inquiry into how failures in its criminal checking system for schools were uncovered by BBC Wales has failed to find who leaked the details.
The council's inquiry began in March
The BBC revealed in February 44 people had not been cleared to work with children in Powys, with the council admitting weaknesses in procedure.
In an attempt to find out who had tipped off the BBC, the council hired an independent investigator.
But after interviewing 37 people, she had not traced the source of the leak.
A report produced by the investigator, Marilyn McCarron, said: "The interviews I carried out and documents I perused do not reveal the source of the leak of the confidential information."
Those she spoke to included 18 councillors and the BBC news website reporter in mid Wales, Carl Yapp.
Ms McCarron added in her report that "uncertainty about the status of such information" may have resulted in an "accidental or innocent disclosure.
"I am therefore unable to place any information or evidence before you which would enable any formal action to be taken against any councillor or officer of the council," she concluded.
The council said it was now planning to "produce a discussion paper" after Ms McCarron suggested it "clarify its procedures" relating to confidentiality of information.
In February, the council had said 39 workers employed before the Criminal Records Bureau (CRB) came into force in 2002 had been overlooked, and a further five had not been checked since then.
Checks started subsequently to obtain CRB clearance for the workers, most of whom were supply teachers.