What happened to Mark Chastain (32), Billy Chastain (30), Mike Sparks (32) and Alex Stevens (29)? On October 9th, the four friends set out for a bike ride in Okmulgee, Oklahoma. However, none of them returned home.

Initial investigations revealed that the men, aged between 29 and 32, were last seen west of Okmulgee at two scrap yards and a gas station. After that, their trail is lost, calls to their mobile phones are forwarded directly to the mailbox, according to the police.

There is now a new investigative approach thanks to an attentive witness: A driver had alerted the police because he had discovered "a male torso in the mud of the Deep Fork River" below a bridge.

In fact, the remains found in the river outside Okmulgee were the missing cyclists - the men had been shot and their bodies dismembered, making identification difficult.

"We believe the men were planning some type of criminal activity," says local police chief Joe Prentice. Investigators don't yet know exactly what they're supposed to have planned. "This theory is based on information from a witness who testified that the deceased were invited to a robbery that would have been worthwhile for any of them," the Okmulgee Police Chief said.

In an interview with Fox 23 TV network, Prentice says one of the men had an app on his phone that gave his last known whereabouts at a junkyard.

The investigators then searched a 25-hectare area on foot and with search dogs - but found "nothing remarkable". However, they found traces of "violent acts" on an adjacent property, according to the police chief.

The owner of the junkyard is a "person of interest" to officials who want to question investigators. However, he has been missing since last Saturday.

Sources: NBC, New York Times, image