CALDWELL — Caldwell Police are working to untangle a case after a man walked into the Canyon County Sheriff's Office Saturday and confessed to killing his stepfather.

The problem? Authorities are not convinced the purported victim was murdered.

Robert Thomas Barnhart, 38, was booked into the Canyon County Jail on a first-degree murder charge after his confession.

Caldwell Police Sgt. Damon Rice said that Thursday afternoon, two days earlier, Barnhart had called paramedics and police to his stepfather's Caldwell home.

The older man, Randall Turner, had apparently had a heart attack, Rice said, a conclusion backed up by paramedics at the scene as well as the coroner's office.

At that point, police say, Barnhart did not say anything that would indicate Turner had died from foul play.

"There was nothing suspicious," Rice said. "The story seemed to match the scene."

But by Saturday, Barnhart's story had changed, and he confessed to suffocating his stepfather the day of his death.

Canyon County Coroner Vicki DeGeus-Morris said that the coroner's office is still reviewing the case, but her investigators have not found anything to support Barnhart's claim.

"There was nothing to indicate a smothering," she said. "There was no sign of a struggle, no marks."

Rice said Barnhart, who has a mental disability, has previously taken responsibility for crimes he did not commit.

"This guy actually has a history of confessing to doing stuff, and then we find out it didn't happen," he said.

In 2016, Caldwell Police tracked down and interviewed several people Barnhart had indicated were his "victims," only to discover no crimes had been committed.

The case is under investigation by Caldwell Police. First-degree murder is punishable by life in prison or the death penalty.

Barnhart remained held in the jail Monday morning, but it's unclear when he will go before a judge. Check back for updates.