According to police, Martinez had allegedly held the boy's head under a hot water tap before authorities were called to the Arizona property.
Once they arrived, Martinez was reportedly waiting outside the home with his wife Romelia where he threw his hands in the air and claimed 'I did it'.
Inside police found the naked boy in bed and unresponsive. He had suffered burns to 15 per cent of his body.
He was wrapped in a towel and rushed to hospital where he was pronounced dead later that day.
According to a complaint filed by the FBI, it's understood Martinez admitted that he'd noticed his son 'acting demonic' in the week following his son's death.
He added that he'd seen a demon inside the boy and was determined to get it out.
It's also reported that the child's mother told police that Pablo had been bathing their son and another child when she heard a gurgling noise coming from the bathroom.
That's when she discovered he was holding the boy under the running water of the hot tap.
She told police he had screamed at her husband to stop before calling a pastor and emergency services.
Pablo had tried to perform CPR and pour cold water over their son but he could not be revived.