Police arrested a graduate of Chuo University on May 21 on suspicion of stabbing his former professor to death in January at the university's campus in Korakuen, Tokyo, police said.

Ryuta Yamamoto, a 28-year-old, part-time worker from Hiratsuka, Kanagawa Prefecture, has admitted to the charges, the Metropolitan Police Department said.

He has reportedly refused to say why he killed Hajime Takakubo, 45, a professor in the Faculty of Science and Engineering. Yamamoto said he did not have any specific trouble with Takakubo, according to the police.

Takakubo was found in a restroom bleeding from more than 60 stab wounds on the morning of Jan. 14. He died shortly after from blood loss, and damage to the heart, lungs and aorta.