The Supreme Court has turned down an appeal filed by death-row inmate and former United Red Army member Hiroshi Sakaguchi of two lower court rulings that rejected his plea for a retrial.

In a decision dated Monday that became binding immediately, the top court's five-justice Third Petty Bench led by Justice Kiyoko Okabe rejected the appeal filed by Sakaguchi, 66, a key member of the extremist group.

Sakaguchi and four other group members killed two police officers and a civilian in the February 1972 seizing of a mountain lodge in the summer resort town of Karuizawa, Nagano Prefecture.

Sakaguchi, along with other United Red Army members, had previously been convicted of killing two fellow radicals who had bolted the group as well as 12 other members at the group's hideouts in Gunma Prefecture.

He has been convicted of killing three and injuring 16 others at the Asama mountain lodge in Karuizawa after taking the wife of the lodge manager hostage.

Sakaguchi and another senior member, Hiroko Nagata, had filed the plea with the Tokyo District Court seeking a retrial of the Asama lodge case, arguing Sakaguchi was not guilty of murder but of negligence resulting in death and injury. Nagata died in jail in February 2011 at age 65.