On January 20, 1985, Gillispie was found fatally shot behind a shop building on his property in northwest Archer City.
Archer County Sheriff Staci Beesinger says, "A call had come into the sheriff's office that he may have been missing. The deputy went by there at about 3 a.m. and he was found at the back of the building laying on the ground."
Gillispie suffered a gunshot to the head and two shots to the chest.
Archer County Sergeant Simon Dwyer is the lead detective in the case.
He says thanks to new technology, computer modeling, and crime scene reconstruction, detectives are learning more about evidence collected at the scene.
"There is fingerprint data, but more interesting is the DNA evidence and some of the other evidence that has come to light," Dwyer says.
"We're looking at all areas of motive. There are several things we can look at, and hopefully we can put all this together and get this case solved," Sheriff Beesinger says.
This case went before a grand jury but no one was ever indicted.
Detectives say since the murder, some witnesses have died, but they're re-interviewing all other witnesses.
And they believe Gillispie's murderer is still alive.
"There's a suspect or suspects, yes," Dwyer says.
"We owe it to the family and to Bill to bring him some justice. Any murder needs to be solved and justice served," Sheriff Beesinger says.
"It's a matter of eventuality, I believe, that we will have the opportunity to bring those responsible to justice," Dwyer says.
Detectives also say they think there are people who know more about this case.
If you do have more information, you're encouraged to call the Archer County Sheriff's Office at (940) 574-2571.
Copyright 2015 Nexstar Broadcasting, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.