A 24-year-old man is under arrest for allegedly killing his girlfriend's baby by feeding him a fatal dose of a kakuseizai stimulant drug in a hotel in the city of Kumamoto, police officials said.

The Kumamoto Prefectural Police arrested Tensho Yoshimura on Sunday on suspicion of murder and violation of the Stimulants Control Law, investigative sources said.

The police suspect Yoshimura, a resident of Mashiki, Kumamoto Prefecture, who is not thought to be the baby's father, took the drug himself and then administered the drug to the baby.