A man believed to be a suspect in the 1971 murder of a police officer during a riot by far-left activists in Tokyo has been arrested for a separate offense after being on the run for over 40 years, investigative sources said Tuesday.

(National Police Agency)

The man, thought to be Masaaki Osaka, 67, was arrested for allegedly obstructing police officers from performing official duties last Thursday when they raided a condominium in Hiroshima, used as a hideout of leftists, while searching for a fellow activist.

Osaka was put on the wanted list the year after the murder of the police officer on Nov. 14, 1971, when about 5,000 students and other activists protesting the ratification of the Japan-U.S. treaty on the reversion of Okinawa staged a violent riot in the capital's Shibuya district.

Osaka at the time was a member of the Japan Revolutionary Communist League National Committee, often referred to as Chukaku-ha, or middle core faction. Hundreds of activists mobilized by the group threw firebombs and attacked policemen, many with iron pipes, and set fire to cars and a police station in the rioting.

The Metropolitan Police Department later arrested Yukio Okumiyama, another member of the group, while placing Osaka on its wanted list for the death of the policeman, 21-year-old Tsuneo Nakamura.

Okumiyama died in February this year after his trial remained suspended since 1981 due to his mental state. The suspension of Okumiyama's trial and his death meant that no statute of limitations of murder was applied to the co-suspects.

The sources said local police from the western Japan prefecture of Osaka, who conducted the raid in Hiroshima, are investigating. The Metropolitan Police Department in Tokyo is expected to investigate the 1971 riot murder case after the man is confirmed to be Osaka.

A 52-year-old member of the group, Tetsuya Suzuki, was arrested together with Osaka in the raid after an arrest warrant was issued for staying at a hotel in January in the western city of Aioi under a false name.

The police believe members of the Chukaku-ha group had provided Osaka with financial support for decades and are looking to trace his movements while he was a fugitive.

The statute of limitations of murder in Japan was 15 years before being abolished in 2010. Okinawa was returned to Japan on May 15, 1972, when the Okinawa Reversion Treaty took effect, from 27 years of U.S. administrative rule.