Confidential papers relating to paedophiles and their victims ended up in a skip after a police sergeant's mother-in-law threw them out by accident, a disciplinary hearing was told.
Martin Skirving-Chehab, from Cleveland Police, is accused of breaching professional standards when he took two carrier bags of material home from a police unit for managing sex offenders in Middlesbrough.
The papers contained sensitive documents about 55 offenders, including their bank details, addresses, car registration numbers as well as information about victims, official statements and CCTV evidence.
The disciplinary panel has heard an inquiry was launched after The Sun ran a story about the leak in June last year, and he told investigators that it had happened due to a "complete fluke" and "an unfortunate set of circumstances".
Mr Skirving-Chehab, who is 42 and has been an officer for 15 years, was asked to remove the carrier bags from the Sex Offenders Management Unit (SOMU) but he took them home.
He kept them unsecured beside his desk at home, before they were put in the kitchen.
The officer received a WhatsApp message from his pregnant wife to say her mother had put the documents in the recycling bin outside.
The hearing heard that his workbook then ended up in a skip outside his home, which was being renovated.
It was found by a dog walker who showed it to his wife and he then passed it on to The Sun which published a story about the security breach.
The paper then returned the documents to the force.
Joan Smith, representing the force, said: "One can only imagine the potential risk to property and life if the information fell into the hands of vigilantes."
Ms Smith told the hearing the experienced officer was well aware of the sensitive nature of the documents he handled.
The force's reputation had suffered as a consequence of the confidential material ending up in a skip, she said.
Cleveland Police contacted all the offenders mentioned in the documents and seven have made a formal complaint, and the force had to step in to answer concerns about their safety following the security breach, she said.
Mr Skirving-Chehab has admitted misconduct but denies gross misconduct.
Giving evidence, he said he was no longer working at the SOMU and was a family liaison officer on murder cases when the breach occurred.
The officer learned that his workbook had been found dumped when a senior officer telephoned him while he was in the maternity unit after his wife had given birth to their first child.
He said he had not planned to pick the documents up from the SOMU on the day that he did, "so I never made any mental space for it".
The officer told the hearing he hoped others could learn from his mistakes, and that he had talked to the data protection manager about putting together training for colleagues.
He said: "I wanted to try to do something positive with this if that was at all possible, otherwise it would have just crushed me completely.
"I never in a million years would have expected this to happen. If I can stop this happening to anybody else, I'll take some comfort."