A passing motorist saw the decapitated head of seven-year-old Jori Lirette, from Louisiana, and alerted police.
Detectives later found the boy's body in a rubbish sack that had been dumped nearby.
The boy's father, 30-year-old Jeremiah Lee Wright, is alleged to have confessed to decapitating his son.
Jori was wheelchair bound and needed a feeding tube having been born with cerebral palsy.
Wright is said to have told police that he did it because 'he'd gotten to the point where he was tired of taking care' of the boy',
Police Chief Scott Silverii said: 'He told us when he put his head out by the side of the road it was so the mother would see it when she came by.'
He said Wright's only explanation for doing so was 'just that he wanted her to feel stupid when she saw the head'.
The crime scene was so gruesome that some of the police who responded to the emergency call have had to have counselling.
Investigators said the grisly killing was carried out over a kitchen sink at the Louisiana home the boy shared with his father and his mother Jesslyn.
His hand and feet were also cut off and discovered nearby in plastic garbage bags.
A forensic team removed the sink from the house in Thibodaux ,Louisiana, as part of their murder investigation.
Wright is understood to have confessed to the killing and is co-operating with police. Read More