A 15-year-old boy who had complained about being bullied at school died in an apparent suicide after falling from a building in Kawaguchi, Saitama Prefecture, investigative sources said Monday.

Shinnosuke Komatsuda, who died Sunday, left a journal entry criticizing his school for its lack of response to his repeated pleas for help, the sources said Monday.

A third-party committee formed by the Kawaguchi Board of Education is looking into the alleged bullying and confirming details about the boy’s death. Officials have not said which junior high school the boy had attended.

According to the sources, a journal entry dated Sept. 6 states: “The board of education are huge liars. They protect the bullies and lie. Why does someone who is bullied like me have to suffer so much?”

The boy’s mother, whose full name has not been released, was scathing about her son’s treatment.

“My son was betrayed by the school, abandoned by the education board and harmed by the perpetrators,” she said after his death. “Please thoroughly investigate the cause, even if from now.”

Shinnosuke began attending the junior high school in April 2016, according to the board of education. According to the sources, the bullying began around May when classmates and older students from his after-school soccer team started to insult and ignore him.

Shinnosuke gave several letters to his homeroom teacher pleading for help in September 2016, but the school’s lack of response apparently led to a suicide attempt at that time, the sources said.

Although his mother then kept him from attending school, Shinnosuke tried to take his life a second time the following month.

In April 2017, he was seriously injured when he jumped off a nearby apartment building in a third suicide attempt, the sources said.

“Even in my second year (at the school), the bullying hasn’t been resolved. I won’t forgive the school and teachers,” a note he left behind at the time said.

Soon after, the school recognized the bullying had been occurring and investigations by the board of education’s third-party committee began in November 2017.

Shinnosuke graduated from the junior high school last March.