Four men were shot and dismembered before their bodies were thrown into a river in Oklahoma, US police have said.
A man considered a person of interest in the case has since disappeared.
Investigators found the first remains of the victims on Friday after a passer-by saw something suspicious in the Deep Fork River near a bridge, Okmulgee Police Chief Joe Prentice said. Their bikes have not been found, he added.
“All four bodies were dismembered before being placed in the river and that is what caused the difficulty in determining identity,” Mr Prentice said.
“The river appears to be a dump site. This is now a murder investigation.”
The victims have been confirmed as Mark Chastain, 32, Billy Chastain, 30, Mike Sparks, 32, and Alex Stevens, 29.
They were reported missing on 9 October after leaving Billy Chastain’s home in Okmulgee on bicycles around 8pm.
Mr Prentice said investigators believe the men intended to “commit some sort of criminal act” that night.
Joe Kennedy, the owner of a wrecking yard, is considered a person of interest in the case after “evidence of a violent event” was discovered on an adjacent property, Mr Prentice said.
Police were led to the area by a ping from Mark Chastain’s phone.
Mr Kennedy has not been named as a suspect in the case, but the police chief said he was missing and asked the public to report any sightings of him.