A 15-year-old boy admitted Friday in his first hearing at the Oita Family Court that he killed three people and left three of their family members severely wounded after breaking into their home and attacking them with a knife, a court official said.
The court decided to keep the boy in custody for about three months to conduct psychiatric tests, the official told reporters.
According to police, the boy said he attacked the family, who lived in his neighborhood, because he was afraid they might tell neighbors he had broken into their house and stolen female underwear.
Judge Yasue Kuga said the boy, whose name is being withheld because he is a minor, will remain detained at Oita juvenile classification office until Dec. 5 while he undergoes the tests.
The hearing was attended by 14 people -- judges, the boy, his parents, lawyers and psychiatrists -- but was closed to the public.
The youth's lawyers argued that it is necessary to conduct a mental examination as they believe the boy's stated motives for the crime do not match the severity of the killings.
The trial is expected to resume after a psychiatric expert examines the boy's present mental state and tries to determine what it was at the time of the attack.
The suspect, a first-year high school student, will not stand criminal trial or face criminal charges because he is under 16.
On Monday, prosecutors sent him to family court.
The teen was arrested Aug. 14 shortly after the attack on the family of Kazumasa Iwasaki, a 66-year-old farmer in the town of Notsu, Oita Prefecture.
Iwasaki's wife, Sumiko, 66; his daughter Tomoko, 41; and Tomoko's son Junya, 13; died from stab wounds.
Tomoko's daughter Mai, 16; her other son Seiya, 11; and Iwasaki himself suffered severe injuries.