HOUSTON (AP) — A father has been charged with fatally shooting his adult son with Down syndrome at a home in East Texas after claiming he had mistaken him for an intruder and then later burning his body in what authorities on Thursday described as a “bizarre crime."

Michael C. Howard, 68, who is an attorney in Houston, told investigators he was at a home he owns in Sabine County on Sunday evening when he accidentally killed his 20-year-old son, Mark Randall Howard, with a shotgun, Sabine County Sheriff’s Office Deputy J.P. MacDonough said at a news conference.

Howard did not call the sheriff’s office until Monday afternoon, about 17 hours after he had used a tractor backhoe to take his son’s body about 2 miles (3.2 kilometers) away to a remote area on his more than 2,500-acre property and placed the body on a wood trash pile and then “cremated” him, MacDonough said. Howard and his son had arrived at the home in Sabine County — located about 170 miles (274 kilometers) northeast of Houston — either Thursday or Friday, authorities said.

Deputies found body parts and bones in the trash pile and sent them to the medical examiner’s office in Jefferson County.

Howard told investigators that the whole thing was a “horrible accident.” MacDonough said Howard told investigators that he "cremated his son in accordance with what he felt his son would have wanted.”

“It is a bizarre crime anywhere you are just because of the nature of the event,” MacDonough said. “Mr. Howard committed this act and in the furtherance of that, burned the body and cleaned the crime scene, which as an investigator, I would take as indicative of nefarious purposes or for nefarious purposes.”

Howard's son had been diagnosed with Down syndrome but was high functioning and did have a job, MacDonough said.

Two days before the shooting, authorities responded to a call Howard made in which he had reported the theft of some property, including a large mower and a trailer. MacDonough declined to say if the thefts might have played a role in Howard thinking his son was an intruder.

Howard remained jailed in Sabine County on bonds totaling $20 million after being charged with murder and tampering with evidence. Authorities said additional charges could be filed.

It was not immediately known if Howard had an attorney to speak on his behalf.