A 23-year-old man in Osaka was arrested Wednesday for allegedly burning his girlfriend's son to death with hot shower water at an apartment.

According to the Osaka Prefectural Police, Takumi Matsubara has denied the charge, telling investigators he and the 3-year-old toddler were only "playing in a hot shower together." Matsubara and the boy's mother were living together at the apartment in Settsu.

When the boy died on Aug. 31, his mother was not at home, the police said. The suspect told investigators he stepped out of the bathroom to set the shower water temperature higher and found the boy collapsed when he returned, they said.

In May, the boy's mother consulted the local government in Settsu about Matsubara allegedly abusing the child, but the city's consultation center concluded the situation at the time did not require any protective measures for the child.