An 18-year-old youth arrested on suspicion of fatally stabbing a 13-year-old boy along the Tama River in Kawasaki has admitted to his role in the slaying, saying he used a box cutter to kill the boy, investigative sources said Monday.

Two 17-year-old boys also arrested in connection with the killing have told the police that the 18-year-old, the alleged leader of their group, murdered Ryota Uemura on Feb. 20, the sources said.

Until Sunday, the 18-year-old had said he would not speak about what happened on that day. The names of all three suspects are being withheld because they are minors.