A third person was present when Kenneth Hudson was fatally shot Monday on Old Shellmound Road near Nickajack Dam, Marion County authorities say.
Jarrod Pickett, 26, is charged with felony murder in the case.
Sheriff Ronnie "Bo" Burnett would not identify the third person but said interviews Friday led investigators to believe a fight broke out between Pickett and the 50-year-old Hudson.
Investigators earlier in the week said a juvenile or juveniles were at the scene of the shooting, but Burnett has refused to discuss that.
All three were in Hudson's truck on the way to his family home when the crime occurred, Burnett said. Hudson was driving, the sheriff said.
The third person, who has not been charged, brought an attorney to the police interview Friday, Burnett said.
"The person has been cooperative, as far as the investigation," the sheriff said. "Now, as far as this person being charged later on, that's something I can't answer."
Authorities now believe Pickett and Hudson began fighting, Burnett said.
"We're not real sure on everything," the sheriff said, "but Mr. Hudson was shot there, and the truck was taken and dumped later on."
Authorities found Hudson's black 1994 Chevrolet pickup truck Wednesday in Dade County, Ga., just over the state line, he said.
The argument took place inside the truck, and the shot was fired at the spot where Hudson's body was found by a mail carrier Monday morning, Burnett said.
"We can't give a reason what the argument was about, but they did have an argument in the truck," he said. "Everything else is not real clear."
He said more interviews are scheduled Monday "that might clear up some more of that."
Pickett faces a preliminary hearing Wednesday in Marion County General Sessions Court, officials said.
Pickett was arrested Wednesday at the Motel 6 on Williams Street in Chattanooga, according to Chattanooga Police Department spokeswoman Sgt. Jerri Weary. Pickett was unarmed, she said.
Pickett is being held without bond until Wednesday's hearing, officials said.
Contact staff writer Ben Benton at 423-757-6569 or firstname.lastname@example.org.