An independent panel looking into a 13-year-old municipal junior high schoolboy's suicide in October 2011 in Shiga Prefecture concluded Thursday that bullying by his classmates was the "direct cause" of his death.

The panel, formed last August, dismissed allegations that the suicide also stemmed from troubles within the boy's family and held the school authority accountable for its failure to prevent the death, because the bullying had been reported by several students.

Upon receiving the final report, Otsu Mayor Naomi Koshi expressed remorse about the panel's "stern conclusion."

While the city of Otsu has maintained three of the boy's classmates were involved in the bullying, the panel exonerated one of them, although they admitted he did play a role in the mental and physical abuse of the victim.

The report said the repeated assaults by the other two classmates, who had been close to the victim, engendered a sense of humiliation and desperation in the bullied boy.

"I feel as though my son's school let him die" even though he repeatedly issued distress signals, the victim's father told reporters Thursday.