Clockwise from top left: Billy Chastain, Mark Chastain, Mike Sparks and Alex Stevens, all of Okmulgee, are seen in this undated handout image provided by Okmulgee police.
CNN  — 

The investigation into four men who vanished after leaving an Okmulgee, Oklahoma, home on bicycles last week is now a murder investigation, the local police chief said, after four dismembered bodies pulled from a river were positively identified as the missing men.

“Although the official cause and manner of death is still pending, each victim suffered gunshot wounds,” Okmulgee Police Chief Joe Prentice said in a news conference Monday. “All four bodies were dismembered before being placed in the river and that is what caused difficulty in determining identities and that’s why it took so long.”

The four men living in Okmulgee – Mark Chastain, 32; Billy Chastain, 30; Mike Sparks, 32; and Alex Stevens, 29 – were reported missing by relatives last Monday night or early Tuesday, Okmulgee police previously said, after leaving Billy Chastain’s home on bicycles around 9 p.m. October 9.

Investigators now believe the four men planned to “commit some type of criminal act,” Prentice said in Monday’s news conference, citing a witness who told investigators they had been invited to join and to “hit a lick big enough for all of them.”

“That is common terminology for engaging in some type of criminal behavior, but we do not know what they were planning or where they planned to do it,” Prentice said.

Additionally, police searched a scrap yard Saturday in Okmulgee, Prentice said. While “nothing remarkable was observed” inside, Prentice said there was “evidence of a violent event” found on an adjoining property.

Prentice said there is a person of interest but no charges have been filed. The person of interest has gone missing as of Saturday night and could be suicidal, Prentice said.

The four bodies were found Friday after a passerby called police about seeing something suspicious. Prentice was notified about the positive IDs on Sunday evening, he said Monday, and the families of the four men were also notified. They had seemed to resign themselves to the fact that the bodies were their loved ones, Prentice said, but news that they had been dismembered was “obviously a shock.”

Police have not recovered any bicycles, nor the gun used in the killings.

“I’ve worked over 80 murders in my career. I have worked murders involving multiple victims. I have worked dismemberments, but this case involves the highest number of victims, and it’s a very violent event,” Prentice said. “So I can’t say that I’ve never worked anything like it, but it’s right up there at the top.”