A copy of a list of gangsters' names drawn up by the Hokkaido Prefectural Police has been leaked, possibly by parties within the police force, it was learned Saturday.

Prefectural police said there was no indication that the list had ever been stolen or lost and they are investigating the case as suspected violation of the Local Public Service Law, which requires that civil servants treat information gained through their work as confidential.

According to the Hokkaido police, the list was compiled by the force's organized crime division using data gathered from police stations across Hokkaido.

Copies of the list -- roughly 1,250 pages thick -- were kept at every Hokkaido police station, officials said. It was updated every few years, with the old versions being collected by the prefectural force and destroyed.