NAGOYA (Kyodo) Police arrested former sumo stable master Tokitsukaze and three sumo wrestlers Thursday in the fatal beating of a 17-year-old wrestler last June.

Tokitsukaza KYODO PHOTO

The ex-stable master, whose real name is Junichi Yamamoto, 57, and the three wrestlers at the stable are suspected of inflicting bodily injuries resulting in the death of Takashi Saito, whose ring name was Tokitaizan.

Yamamoto has admitted to beating Saito but denied he instructed senior wrestlers to punish him, investigative sources said.

Yamamoto allegedly hit Saito over the head with a beer bottle last June 25 at the stable in Inuyama, Aichi Prefecture, after the wrestler tried to flee. The ex-stable master is suspected of ordering the three senior stablemates to assault Saito, including beating him with a metal baseball bat, the sources said.

The next day, Saito underwent full-contact practice at the stable and lost consciousness. He was taken to a hospital but died.

After Saito grew exhausted, Yamamoto kept the seniors away from him. Despite the teen's deteriorating condition, he waited before calling an ambulance.

Aichi Prefectural Police admitted Thursday their initial investigation into Saito's death was "insufficient."

Despite calls for an autopsy, they first treated Saito's death as "heart failure" and ruled out foul play — even though his corpse bore severe bruises.

"We should have thoroughly investigated the cause of (Saito's) death and carefully judged whether it constituted a criminal case," Inuyama Police Chief Yukio Tsuzuki told a news conference following Yamamoto's arrest.

The Japan Sumo Association fired Yamamoto in October.

Nagoya University recently confirmed in an autopsy that Saito died from multiple traumatic shock. The same conclusion was reached last year in an autopsy conducted by Niigata University.

The family of the victim said they were shocked to see the cuts, bruises and burns covering their son's body.

But Yamamoto first insisted to the family that the injuries were the result of "regular training," the family said.