A Sapporo court on Friday sentenced a 54-year-old man to six years in prison for killing a female university student at her request and then mutilating her corpse.

In handing down the ruling, the Sapporo District Court rejected the argument by defendant Isamu Ono's legal team that he was of diminished mental capacity and should receive a suspended sentence over the October 2022 killing of the 22-year-old student at his apartment. The prosecution had sought nine years in jail.

Presiding Judge Hideki Igeta ruled Ono can be held fully responsible for his actions given they were premeditated. He said his failure to attempt to dissuade the student from seeking to end her life was "disregarding life, antisocial and extremely malicious."

Photo taken on March 17, 2021, shows the Sapporo District Court. (Kyodo)

Speaking through a representative after the ruling, the bereaved family of the student, Yuina Segawa, said they had "raised our daughter as best we could."

"We want the defendant to never forget this incident and repent for his sins for even a short time," the statement said.

According to the ruling, Ono suffocated Segawa sometime between Oct. 4 and 5 of 2022 at his apartment in Sapporo in Japan's northernmost prefecture of Hokkaido. The ruling stated he also used a blade to mutilate her body on Oct. 6.

The prosecution said during the trial that the two started exchanging messages online in early September last year after Segawa wrote "kill me" in a social media post and Ono "liked" the message.

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