A criminal court jury deliberated four hours Friday before ruling Chet Allen Walker guilty of first-degree murder in the Feb. 10, 2001, slaying of 20-year-old Joshua Shane Swafford.
Judge Steve Bevil then sentenced Walker, 21, to a life prison sentence.
He faces sentencing on Aug. 27 at 10 a.m. for burning personal property and abuse of a corpse.
Walker, who had sobbed during much of his testimony, took the verdict without emotion.
But his mother, Eva Duncan, had to be carried from the Courts Building.
Judge Bevil let the Walker family out of the courtroom first, and told the Swafford family to leave later.
Walker had admitted killing Swafford, but the defense said it was "in the heat of passion" and was not premeditated.
Walker said he had given Swafford $1,700 in cash to buy two pounds of marijuana that night. He said they went to a house in Hixson, but Swafford told him he was not going to get his money back or any drugs.
He said Swafford put a semi-automatic weapon to his head, saying, "You're going to take it like a bitch."
Walker said after they got back in the car that he took the gun from where Swafford had put it under the seat. He said he told Swafford to drive on after he let his cousin, Barry Dent, out at his house on Smith-Morgan Road at Soddy-Daisy.
He said he again asked Swafford for his money, and he said he wasn't getting it back.
Walker said he then fired out the window once, then turned and emptied the weapon on Swafford.
He said he stayed in the vehicle with the body as Swafford died, trying to decide what to do. He finally decided to set the vehicle on fire.
Chris Poole handled the case for the state.