The North Texas couple accused of burying their special-needs son in the backyard of their Burleson home told police the 26-year-old had died a few days before at a local hospital, officials said.

The Burleson Police Department is investigating the death of Jonathan Kinman. His mother, 47-year-old December Marie Mitchell, and stepfather, 50-year-old Jonathan James Mitchell, are charged with tampering/fabrication of physical evidence with intent to conceal a human corpse.

“It’s a very heartbreaking situation,” said Deputy Chief Doug Sandifer with the Burleson Police Department.

Sandifer said a family friend reached out to police Oct. 14 after seeing a Facebook post from December Mitchell about her son’s death. Kinman had Russell-Silver Syndrome — a rare genetic disorder — as well as autism, according to court documents.

Officers conducted a welfare check at the family’s home in the 400 block of White Oak Lane later that day. December Mitchell told them her son had died at Texas Health Huguley Hospital, Sandifer said, but investigators discovered the hospital didn’t have a record of his death.

“Nothing was adding up,” Sandifer said.

Detectives spoke with December Mitchell again, and she told them she didn’t have medical paperwork on Kinman’s death. She also said they weren’t planning a funeral “due to cremation of Jonathan,” a search warrant affidavit obtained by the Star-Telegram states.

The evening of Oct. 14, Jonathan Mitchell called 911 to say his wife had buried Kinman in the backyard, and he’d just found out about it, according to the affidavit. Police returned to the house and found several locations where a body might be hidden.

December Mitchell immediately told the officers she wouldn’t answer any more questions without an attorney present, the affidavit states. A friend of the family informed police that December Mitchell told him Kinman had recently died and been buried in the backyard. The friend advised the couple that if they didn’t call police, then he would.

“This correlates with the timeframe of Jonathan Mitchell calling 911 to report (December Mitchell) had reportedly buried Jonathan in the backyard of the home,” the affidavit states.

December Mitchell and Jonathan Mitchell were taken into custody. As they were sitting in the back of a patrol car, they could see cadaver dogs searching the property, investigators said. December Mitchell was caught on the patrol car’s camera saying, “The dog was going in find him on me … it was all me … that dog was going in to find him,” according to the affidavit.

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Burleson police and Texas Rangers returned to the home Oct. 15 and made an extensive search of the property. They finally found Kinman’s body, wrapped in a camouflage blanket and lying in a shallow grave by one of the sheds, investigators said in the affidavit.

Neighbors who had lived near the family for about two years told Star-Telegram media partner WFAA-TV they didn’t know the couple had a son.

“Never saw him go in the house or out of the house,” one woman said.

Family members of Kinman’s biological father said in a statement that they were horrified at the news.

“This is a living nightmare for the Kinman family,” the statement reads. “Please know that we are in full cooperation with law enforcement and we will fight for every last ounce of truth and justice to come to light for the sake of our sweet boy.”

The Tarrant County Medical Examiner will conduct an autopsy and determine the cause of Kinman’s death. Sandifer said the results are still pending.

December Mitchell and Jonathan Mitchell are being held in the Johnson County Jail on $250,000 bonds, according to jail records.