A Criminal Court jury from Nashville on Tuesday afternoon found Frank Casteel guilty of the 1988 Signal Mountain murders.
Casteel, who had been convicted in 1998 and then given a new trial, will go back to state prison to resume serving three concurrent life sentences.
The jury at the Courts Building in Chattanooga deliberated over four hours Tuesday and another four hours today.
He was found guilty of first-degree murder in the deaths of Richard Mason, Kenneth Griffith and Earl Smock.
Casteel showed no emotion. His wife, Suzie, and sons, Trevor and Donnie, left the courtroom as soon as the first guilty verdict was announced.
Family members of the victims said they were glad the long case "is finally over."
Paula Mason Griffith Kirby, daughter of Richard Mason and widow of Kenneth Griffith, said, "I feel the same as last time - just glad it's over with." She was handed by District Attorney Bill Cox the photo of her slain husband that was shown to the jury.
Lee Griffith, brother of Kenneth Griffith, said, "We finally can put this behind us and get on with our lives. I am going to go on with enjoying my grandchildren and raising my children. We don't have to worry about this ever again."
He added, "I am very pleased with the way the attorney general and (special prosecutor) Lee Davis handled the case and thankful for the way the jury reacted.
"Now I know my baby brother's proud. We got him."
Emma Griffith, mother of Kenneth Griffith, said, "Justice has been done finally."
Larry Sneed, retired county detective who worked on the case for years, said he believes the killings occurred when the trio confronted Casteel.
He said, "Kenneth was shot first, and he kept on till he got them all. He pulled the bodies to the side and hid them until dark, then he had help moving them."