Police arrested a 14-year-old male junior high school student on Saturday on suspicion of stabbing a classmate to death while studying together in Tokorozawa, northwest of Tokyo.
The student was held for attempted murder after the police found Kotaro Hongo, 13, on Friday just outside the suspect's home with multiple stab wounds to his upper body following an emergency call, the police said.
He was taken unconscious and in critical condition to a hospital but died of his wounds early Saturday.
The police believe the two began quarrelling while studying together at the 14-year-old student's home Friday afternoon. His grandmother was at home at the time.
The police said the 14-year-old boy has admitted to the stabbing, telling them that they had "a quarrel about a textbook." He initially told police officers arriving at the scene that Kotaro had committed suicide.
Another student who was on his way to join them to study for their final exams found Kotaro lying in front of the home and asked a nearby resident to make an emergency call, according to the police.
The head of the local education board held a press conference and said the students' school was not aware of any personal trouble between them.
They had known each other before joining the school and both belonged to the school's table tennis club.
A 14-year-old girl at the same school said the two appeared to get along well. She said she had never seen them argue.