OKMULGEE, Okla. (KFOR) — Remains found in an Oklahoma river have been identified as belonging to the four men who went missing last week in Okmulgee.

One week ago, family members reported 32-year-old Mark Chastain, 30-year-old Billy Chastain, 32-year-old Mike Sparks, and 29-year-old Alex Stevens missing. The Okmulgee Police Department said all four were close friends and were believed to have left Billy Chastain’s house on bicycles on Oct. 9.

On Friday afternoon, search crews stumbled upon human remains in a river southwest of Okmulgee.

On Monday afternoon, Okmulgee authorities announced the remains had been positively identified as the missing men.

“This investigation is now a murder investigation,” said Okmulgee Police Chief Joe Prentice.

Prentice said all four men suffered gunshot wounds and were dismembered before their remains were thrown in the river.

“That is what caused difficulty in determining identity,” he said, adding that the river appears to have been used as a dump site.

Prentice said they are still trying to determine a timeline for the murders, but investigators believe the bodies were dumped early last Monday.

Before the group went missing, Prentice says he believes that the men were planning to commit a crime, according to a statement from a witness.

“We do not know what they planned or where they planned to do it,” he said.

Investigators said they searched a salvage yard where one of the men’s phones was tracked, but they didn’t find anything there. However, Prentice says evidence of a “violent event” was found at a nearby property.

The owner of the salvage yard, Joe Kennedy, is now considered a person of interest in the case, but has not been officially named as a suspect. Officials said Kennedy has gone missing.

Prentice said during previous interviews, Kennedy has denied knowing the men.

Police said they are also still searching for the missing bicycles.

“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,” said Prentice. “So I can’t say that I’ve never worked anything like it, but it’s right up there at the top.”

Anyone with any information about the murders, or Kennedy’s location, is asked to call (918) 756-3511.