Police said Sunday they have arrested three 14-year-old boys for allegedly beating a homeless man to death Friday night at a "gateball" ground in the northwestern Tokyo city of Higashimurayama.
The police have also notified a juvenile counseling office that a 13-year-old boy is suspected of being involved in the assault on the homeless man, Kunihiko Suzuki, 55.
Under Japanese law, children under 14 cannot be held criminally responsible for their actions.
The four, classmates in their second year at a junior high school in the city, turned themselves in at a police station Saturday night. The three were arrested shortly afterward, the police said.
Suzuki was pronounced dead at a hospital in the early hours of Saturday after being beaten by a group of boys between 9:20 p.m. and 11 p.m. Friday at the gateball ground in the city's residential area, the police said.
The boys dragged Suzuki, who was sleeping in a rest area in a facility in the park with two other homeless men, to a vacant lot about 10 meters away and began assaulting him, the police said.
The students told investigators they attacked Suzuki because he had beaten three of them in a city library last Thursday, police sources said.
They said Suzuki beat the three after they made a noise in the library. One of the four followed the homeless man and learned that he was sleeping in the gateball park.
The police suspect other boys were involved in the assault and are searching for them.
One of the other two homeless men sleeping in the facility notified the police after the boys fled.
Suzuki had lived in the park for at least a year, the police said.
Gateball, a game developed in Japan, is modeled on croquet and mainly played by senior citizens.