The Osaka High Court on Wednesday upheld a lower court ruling against a 19-year-old male sentenced to 12 years in prison for robbing and murdering a taxi driver in Hyogo Prefecture in 2000.
The male was 16 at the time of the incident and his identity has been withheld.
The court rejected a claim by the defense that the youth was temporarily insane at the time of the crime. It agreed with the September 2002 ruling by the Kobe District Court's Himeji Branch that he was fully competent to be held liable.
"While being a minor, it was a crime that was carefully planned and the method of murder was cruel," presiding Judge Shunsuke Imai said.
The youth's lawyer said he will talk with his client before deciding whether to appeal the latest ruling.
The youth ran away from home with his girlfriend and decided to murder a taxi driver because he ran out of money.
He stabbed Fumio Sammi, 49, in the neck with a knife on the evening of Dec. 27, 2000, in Mitsu, Hyogo Prefecture, and stole about 18,000 yen in cash.
The girlfriend has been sent to a juvenile reformatory.
"I cannot understand why the ruling ignored the evidence that the youth had split personalities," said his lawyer, Koji Ishii. "I am worried about the youth returning to society (in the future) without receiving treatment."