Sequoyah, Okla. (CNN) -- Oklahoma authorities investigating a mysterious death have come up with a rare theory.

They are looking into whether or not a 65-year-old man died from spontaneously bursting into flames.

"This is a case that I've never seen before."

Family members found 65-year-old Danny Vanzandt dead Monday inside his home on Bawkin Road outside Muldrow.
"The body was burned and it was incinerated."

Sheriff Ron Lockhart says he believes the death could be a rare case of spontaneous human combustion.

"I think there's only about 200 cases worldwide, and I'm not saying that this has happened, I'm just saying that we haven't ruled it out," Lockhart said.

Lockhart says the fire didn't damage the house and there were no signs of struggle.

"There was no damage to the furniture or anything around the fire, so it was a low heat fire."

The family says they noticed the back window of the man's pickup truck was busted out.

Investigators sent the body to the medical examiner's office in Tulsa.

"If you read about spontaneous human combustion, that's what we have here."

The sheriff says Vanzandt was an alcoholic and avid smoker.

We asked if it's possible Vanzandt accidentally killed himself some other way, like dropping a cigarette on himself.

"And a cigarette burn will not do that," says Lockhart.

The autopsy report is pending.