Prosecutors have submitted an opinion to the Supreme Court claiming that rulings by lower courts in a 1991 double murder case in Hokkaido, in which the defendant was sentenced to life in prison, violated the common law standards of the death penalty, it was learned Wednesday.

Prosecution authorities have made similar claims to the Hiroshima and Tokyo high courts in cases in which the death penalty demanded by prosecutors had been commuted to life in prison, informed sources said. The move is regarded as an apparent effort by prosecutors to pressure judicial authorities who "tend to dodge doling out capital punishment," the sources said.

In the past, prosecutors appealed to the top court only in three cases in which a high court sentenced a defendant to life in prison. The exception is the Nagayama case, in which the accused was executed in August.

In 1981, the Tokyo High Court sentenced Norio Nagayama to life in prison for shooting four people dead in 1968 in Tokyo, Kyoto, Hokkaido and Nagoya. He was sentenced to death at the same court in 1987 after the Supreme Court returned the case to the court in 1983. The top court supported the decision in 1990 in the appeal.