HILO, Hawai'i — A 29-year-old Japanese national was convicted of manslaughter yesterday for stabbing his boss to death at the Hama Yu Japanese Restaurant in Waikoloa last year.

Prosecutors had charged Yasushi Kato with second-degree murder in the slaying of 61-year-old restaurant owner Yukichi Ito, but a Hilo jury convicted him of the lesser manslaughter charge after finding Kato was under "extreme mental and emotional distress" at the time of the slaying.

Kato faces a mandatory 20-year prison term when he is sentenced by Judge Glenn Hara on Jan 12.

Ito suffered more than 20 stab wounds as he tried to fend off his attacker, according to the testimony.

Juror Lillian Lee said after the trial that the jury spent more than three days studying evidence and was influenced by the testimony of two mental health experts who said Kato was suffering extreme mental distress at the time of the killing.

That testimony was supported by the testimony of a forensic pathologist who studied Ito's many stab wounds, "and corroborated the emotional state of Mr. Kato," Lee said.

Kato testified that he did not remember much about the attack, although he did at one point testify that he remembered stabbing Ito.

Prosecutors argued Kato knew what he was doing and planned the killing. The two men argued the day before the slaying, which took place March 23, 2004, and testimony at the trial was that Kato told a psychiatrist that he wanted to kill Ito, said Deputy Prosecutor Sandra Freitas.

Kato, who did not have a permit to legally work in the United States, testified that Ito took him aside the day before the slaying and told him he could no longer work at the restaurant in the Kings' Shops in Waikoloa.

Kato testified during the six-week trial that Ito made statements Kato believed were threatening, but Freitas said there was no other testimony that Ito ever threatened Kato.

Kato took his 17-inch sushi knife home, and returned to work with it the next day. At about 4:30 p.m., during the break between the lunch and dinner shifts, Kato attacked Ito at a counter, stabbing him twice in the neck, and then continued to stab Ito after he fell to the floor.

Prosecutors had wanted a murder conviction against Kato and a finding that the killing was "heinous" in nature, which would have made it possible to have Kato imprisoned for life without possibility of parole.

Reach Kevin Dayton at kdayton@honoluluadvertiser.com.