The Osaka Prefectural Police have improperly stored documents and other evidence linked to about 5,000 criminal cases at their police stations, allowing the statute of limitations for more than 80 percent of the cases to expire, officials said Monday.
The problem was uncovered when officials opened an investigation into the way the police were handling their files following the discovery of improper care at one police station.
The probe expanded to find similar problems at 61 of the 65 police stations in Osaka Prefecture.
"Because high-priority cases are investigated first, the handover (of cases from outgoing police officers to incoming ones) has tended to be neglected," a police official said.
The police have been combing through their records after boxes filled with files and evidence from investigations spanning 1996 to 2012 were found in a machine room at Habikino Police Station in eastern Osaka in 2014.
Of the 5,000 cases for which documents and items of evidence were found stored improperly, about 4,300 involved cases for which the statute of limitations had already lapsed while the files and evidence sat abandoned.
In about 1,000 of the expired cases, suspects had nearly been identified. But most of the cases involved assault and embezzlement, rather than murder and other more serious crimes, according to the officials.
Many of the roughly 10,000 items that were stored improperly were found inside heating rooms and storage rooms in police stations. Some dated as far back as over 30 years ago.
Laws governing criminal prosecution stipulate that evidence and files on a case must be sent to prosecutors. Of the roughly 5,000 cases in question, 1,700 have been sent to prosecutors, according to the officials.
The number of improperly stored files could rise as the police finish compiling their findings in the next few months.