Police arrested a man Tuesday on suspicion of having caused injuries resulting in the death in September of his girlfriend's 3-year-old son, Ryutaro Yamada, in Tokyo.
Yuji Watanabe, 34, the partner of the boy's mother who lived with them both, had said he found Yamada floating face-down in the bathtub after a short unsupervised period.
But autopsy results showing no water in the boy's lungs seemed to contradict Watanabe's account, prompting authorities to investigate whether the man had subjected the child to violent abuse and tried to cover it up as a drowning accident.