"One shot in the back (of the head), two in the front," Bebb said. "That's what I've been told."
Bebb told the News Sentinel that Monroe County Deputy Sheriff Kenny Hope, who has been placed on administrative leave in connection with the investigation, is not classified as a suspect. Bebb said it is too early in the case to be reaching any conclusions.
"We are just checking out any information we get, but we are not going to develop tunnel vision," he said.
Miller, 60, of Sweetwater, was president of an excavating company. He was also active in local Republican politics and community affairs.
He has been missing since around 12:30 to 12:40 p.m. Saturday, when he left the election commission office. It is believed that he was headed home.
Around 8 p.m. that night, a Monroe County deputy found Miller's Ford Crown Victoria off Sands Road, fully engulfed in flames.
Hope is not the deputy who found the car, Bebb said.
The burned body tentatively identified as Miller was found in the trunk.
Monroe County Sheriff Bill Bivens immediately asked for the Tennessee Bureau of Investigation to be brought into the case, Bebb said. The State Bomb and Arson Section is also investigating.
Miller had a handgun carry permit and a commission as an auxiliary deputy for Loudon County, according to Loudon County Chief Deputy Tony Aikens.
It is not known if Miller was armed on Saturday.
Aikens, who was a friend of Miller, said Miller once told him that his car contained a police radio with Monroe County emergency frequencies.
On Thursday, a TBI spokeswoman announced that the body had been "tentatively" identified as Miller but that further tests are needed to make a positive ID.
The investigation is proceeding on the likelihood that the victim is Miller.
"We want to find out who killed Jim Miller, and of course, why he was killed," Bebb said