Turney yelled at Gumm, made an obscene gesture and followed him to the parking lot, the affidavit says.
Gumm parked his 1992 Honda, and Turney parked his 1991 Ford Escort behind him, blocking Gumm's car, according to the affidavit.
Turney then walked toward Gumm, who got out of his car holding his .38-caliber Smith and Wesson revolver, the affidavit says.
Gumm described Turney as being in a rage and told police that Turney said, "You're history," according to the document.
Gumm told investigators that he took that statement as a threat against his life, the affidavit says.
Police had said after the shooting that Gumm said he warned Turney that he had a gun and that because of health problems, he couldn't run away or fight him.
Gumm also told investigators that he "backed away from Turney approximately two times around his (Gumm's) car" before Turney pushed his shoulder, according to the affidavit.
Turney was shot once in the chest during the confrontation. He was taken to St. John Medical Center, where he was pronounced dead.