James Alex Hurley had been living with his grandparents and their children when he was found dead in their living room.
Video footage obtained by police showed the 12-year-old boy, from Montana in the United States, had allegedly suffered a pattern of abuse that included forced exercises and other physical abuse.
James Sasser jnr, together with his partner Patricia Batts and their teenage son, the young boy's uncle, have all been charged with deliberate homicide following James' death, reports news.com.au.
The young boy was living with his grandparents and their children, including their 14-year-old son, for two years before his death.
According to court documents obtained by Chicago's WGN-TV, detectives found video from about two years ago where James "appeared to be a healthy and well fed boy", but at the time of his death, detectives said James "appeared to be emaciated".
The family reported James' death on February 3 and when police arrived they found him with multiple wounds and contusions over his body, prompting them to contact homicide detectives, People reported.
Local authorities told KTVH-TV that "systematic torture and beatings" led to James' death.
The family are accused of withholding food from the boy and forcing him to do exercises like jumping jacks and squats that were allegedly recorded by the family on video, the publication reported.
James was sent to live with his grandparents by his mother after his father died in 2018.
But he didn't appear to have a stable relationship with his teenage uncle. The pair fought often, with the last one being on February 2, WGN-TV reported.
James' grandmother, Patricia Batts, allegedly told investigators that on February 2, during the Super Bowl, she was asleep but woke to find her grandson was being hit by his uncle with a paddle during an altercation. She later found James' body in the living room area.
An autopsy revealed James' preliminary cause of death was blunt force trauma to the back of his head.
JAMES' "ERRATIC" BEHAVIOUR
According to a criminal complaint from the Gallatin County Attorney's Office, the family described James as having "suicidal" and "erratic" behaviour, and also "hearing voices".
But despite the family's claims, detectives have not been able to find any record of the family reporting these behaviours to law enforcement or to have sought any medical attention for James, WGN-TV reported.
After the three arrests, authorities charged a second teenager, Gage Roush, 18, with assaulting James.
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