A 68-year-old death-row inmate convicted of serial bombings at companies in 1974 and 1975 has died of multiple myeloma at the Tokyo detention house, the Justice Ministry said Wednesday.

Masashi Daidoji, a member of the extremist Higashi Ajia Hannichi Buso Sensen (East Asia Anti-Japan Armed Front), was convicted of bombings that included the August 1974 attack on the headquarters building of Mitsubishi Heavy Industries Ltd. in Tokyo. That attack left eight people dead.

Daidoji was among a number of leftist militants arrested in 1975 on charges of conducting a bombing campaign against Japanese companies to condemn Japan's military and commercial advance in East Asia before and after World War II.

Although the Supreme Court sentenced him to death in 1987, he had appealed multiple times for a retrial, arguing that a new examination of the bombs used in the Mitsubishi Heavy attack had shown he had no intention of killing the victims.

The extremist group also targeted the headquarters of trading house Mitsui & Co., construction firm Taisei Corp. and synthetic fibers maker Teijin Ltd.

In connection with the serial bombings, nine people were arrested and one committed suicide. Six, including Daidoji, were convicted.

Some of the arrested were released as extrajudicial measures taken after the Japanese Red Army hostage crisis in Kuala Lumpur in 1975 and the hijacking of a Japan Airlines jetliner in the Bangladesh capital of Dhaka in 1977.

Daidoji along with Toshiaki Masunaga, also sentenced to death for the 1974 bombing, had sought compensation from the state, claiming in 2004 that the Tokyo detention house did not allow supporters to provide the two with letters, cash and other materials.

The practice was later corrected and a district court ordered the state in 2008 to offer a symbolic payment to the two of ¥10,000 each.