Okmulgee missing men: Remains found in river amid search for 4 friends who vanished in Oklahoma

OKMULGEE, Okla. -- Police announced Friday that officials have found what appears to be human remains partially submerged in a river amid the mysterious disappearance of four close friends in Oklahoma.

Mark Chastain, 32; Billy Chastain, 30; Mike Sparks, 32, and Alex Stevens, 29, were last seen leaving one of their homes in Okmulgee around 8 p.m. Sunday reportedly riding bicycles, according to the Okmulgee Police Department.

The families of the missing men have been notified of the discovery, ABC News reported.

Okmulgee Police Chief Joe Prentice said he's unsure if the remains are connected to the four missing men.

Prentice said it will take a while to remove the remains from the river. He added that the remains look to be human bodies.

Authorities are working to document the scene and they will start the recovery process from the river.

Both of the Chastain men and Sparks were reported missing by one of their spouses during the overnight hours on Monday, police said. Stevens' mother contacted authorities a few hours later to also report her son's disappearance.

Police spent Tuesday and Wednesday interviewing potential witnesses, working to gather descriptions and canvassing areas to confirm reported sightings.

"These men are exhausted," Police Chief Joe Prentice said in a Facebook post shared on Wednesday. "I am sending them home to get rested and we will start fresh tomorrow, unless something time-sensitive comes in overnight."

According to investigators, two of the men were believed to have cellphones with them, however, attempts to contact them go straight to voicemail.

Chastain's cellphone was tracked to an area south of Okmulgee, but was turned off or lost power at some point. Officers checked the area, but found no sign of the men, police said.

Anyone with information regarding their whereabouts is urged to contact the Okmulgee Police Department.