MANNFORD, Oklahoma - Investigators need the public's help to crack a Creek County murder. 

It's been nearly 20 years since a Mannford father was found shot in the back of the head. 

The Oklahoma State Bureau of Investigation featured the case Monday, releasing a Cold Case Playing Card on its Facebook page.

It's one of 52 cases they're hoping to solve. 

The body of 48-year-old George Campbell was found inside his vehicle, parked on Pelican Point Road the night before Father's Day, June 22, 1998.

Authorities tell News On 6 he was slumped over the steering wheel, with gunshot wounds to the back and side of his head. 

Campbell was an engineer in Tulsa, designing flight simulators.
The avid OSU fan had two grandchildren. We talked to the family one year after the murder.

"We were told about four days after it happened that they had some good leads, that they had witnesses, and that type of thing. We thought it would progress fast, but it didn't," said Brent Bruner.

There's still no closure for the family.

At the time, they were offering a $10,000 reward for any information leading the arrest of whoever killed Campbell. 

The OSBI is asking for anyone with information to call 1-800-522-8017.