The father, 31-year-old Pablo Martinez, was arrested after he told investigators what he did at his home on the Pascua Yaqui Tribe reservation on Thursday.
Martinez told authorities he noticed his son had "a demon inside of him" during the past week, and when he was giving him a bath, he "saw something evil" inside his child, KGUN reported. Thinking he "had to cast the demon out," Martinez allegedly held the boy under running hot water for five to 10 minutes.
Romelia Martinez, the man's wife and the boy's adopted mother, said she heard a gurgling coming from the bathroom, where she found the boy being held under the faucet, and screamed at Martinez to stop. She dialed 911 before Martinez poured cold water over the boy and reportedly attempted CPR on him.
When investigators arrived on scene, Martinez allegedly told them they "were not in the right mindset or belief" to understand why he allegedly did what he did, and eventually told police "something to the effect of 'I did it,'" the news outlet reported, citing a criminal complaint.
The boy was transported to a hospital, where he was pronounced dead with burns covering 15 percent of his body.
Martinez was charged with first-degree murder. The father is not a member of the Pascua Yaqui Tribe, but Romelia Martinez is, according to reports.