Hideaki Kumazawa, 76, was arrested in June on suspicion of killing his 44-year-old son, Eiichiro, after calling the police and admitting to stabbing him in the neck and chest at their home in Tokyo.

Kumazawa, a retired agricultural vice minister and former envoy to the Czech Republic, told cops at the time he “thought my son might harm others” after finding out about an unconnected stabbing rampage two days earlier that resulted in two people dead and 17 wounded, according to Kyodo News.

He later pleaded guilty to the crime during the trial.

“I think it is my duty to pay for the crime and pray that my son can spend a peaceful time in the afterlife,” Kumazawa said Friday during the closing court session, Kyodo News reported.

During the trial, Judge Tomoyuki Nakayama said the son’s body had more than 30 stab wounds, including some that were very deep, indicating that the killing was not purely self-defence. The son died from massive blood loss.

Prosecutors had sought an eight-year prison term while defence lawyers instead pursued a suspended term, claiming Kumazawa killed the 44-year-old in self-defence after the son’s threat.

Witnesses say the attacker carried a knife in each hand and slashed school children at a bus stop in Kawasaki, Japan.

His son had a developmental disorder and was routinely violent toward his mother. He was removed from his parents and lived alone in an apartment until he returned home a week before the killing.

The Tokyo District Court said in its ruling that the son resumed his violence as soon as he returned home and threatened to kill his father.

In its ruling, the court said that Kumazawa feared his son might harm others as in a case days earlier, when a man described as a social recluse — known in Japan as “hikikomori” — stabbed a number of schoolchildren at a bus stop outside Tokyo, killing two people and wounding 17 others, mostly schoolgirls, before killing himself.

The court ruled that Kumazawa deserved a more lenient six years in prison, taking into consideration his effort to improve his family’s relations with the son, the violence inflicted by his son and the threat of being killed.

The case and the earlier attack in Kawasaki highlighted growing concerns about “hikikomori.”

A government survey in March showed there are an estimated 610,000 “hikikomori” between the ages of 40 to 64 in Japan, mostly men, with many still taken care of by their elderly parents without proper support from the outside.