ROCK ISLAND -- Four days after he was reported missing in October 1990, Jerry Wolking's Chevrolet Suburban was found in the parking lot of the Quad City International Airport.
Investigators found blood inside and outside the vehicle, along with dirt and mud.
There was no evidence Mr. Wolking left on a flight.
Fast forward to the spring of 2013. For 23 years, a sack of evidence remained in the Moline Police Department's evidence locker, evidence that today could be the key to solving the assumed murder.
On Monday, Detectives Michael Griffin and Scott Williams were inside Augustana's Fryxell Geology Museum with Professor Michael Wolf and his student, Grant Wick.
Since the spring of 2013, Detective Griffin has been working with the professor and the student to try to solve the case by means of forensic geology.
Detective Griffin has photos of Mr. Wolking's Suburban when it was found 23 years ago at the airport. Some of the pictures show the trailer hitch ball mount of the vehicle caked in dirt and mud. That was unusual for Mr. Wolking to have that on his vehicle.
"His truck had soil compacted on it," Detective Griffin said. "For background, Jerry Wolking, he was a very clean person. He was president of a car club.
"He kept his vehicle in very immaculate condition."
Numerous leads were followed at the time of Mr. Wolking's disappearance. The blood in the vehicle was identified as Mr. Wolking's, Detective Griffin said, but the soil was a clue that had never, until now, been tested.
Knowing the Illinois State Crime Lab was overburdened with day-to-day cases, Detective Williams said it could be years before getting any kind of response on the Wolking case.
Saying he was just playing a hunch, Detective Williams had a conversation with Mr. Wolf, a friend, and asked the professor if he thought something could be done with the bag of dirt collected from the vehicle.
"He said, 'actually, there's a lot that can be done,'" Detective Williams said.
Detective Griffin said the detectives in 1990 probably didn't know what they had when collecting the soil as evidence.
"But, they had the wherewithal to secure the evidence," Detective Griffin said.
On a table inside a science lab at the college, the student and the professor explain some of science they are using to find out where Mr. Wolking's body may have been buried. It's a first-time collaborative effort between the college and the Moline Police Department to try to solve a cold case.
The work with Augustana comes after Moline police renewed its investigation into Mr. Wolking's disappearance in April. Using information from interviews and other leads, the police used a backhoe and end loader, along with cadaver dogs from Madison, Wis., at a wooded area near Milan.
In June, police focused the search in Green Valley Park in Moline.
Detective Griffin said the suspect in the case had ties to the Milan location. He said some people have come forward, also giving statements that they saw a vehicle matching Mr. Wolking's Suburban in the Green Valley area at the time of his disappearance.
Mr. Wick has until May, the month he graduates, to complete his studies of the soil samples and, perhaps, help determine if either of those locations is a likely place to search again.
The professor pointed to a map of Rock Island County and the various soil compositions.
"If Grant does a good enough job and really identifies that material and says, 'it's a yellow silt loam and the location of interest is here, that could help pinpoint it,'" Professor Wolf said. "There are different compositions of soil. Hopefully, he'll be able to identify and key it to the soil chart."
The soil on the Suburban can then be matched to the location where Mr. Wolking's vehicle was. If the soil types match at the locations in question, the body could have been there.
"My goal is to try and connect it (dirt) with other soil samples we've taken in the area of the suspect," Mr. Wick said.
"This is a new setup for Grant," Professor Wolf said "He's been using the binocular scope to look at samples, and now a digital camera, which will help document the similarities. We can put this evidence right next to the other samples and visually inspect."
For the Moline police, the work the student and professor have provided is critical to the investigation.
Detective Griffin said he is in contact monthly with Mr. Wolking's son and daughter in the area.
"They really want closure, obviously," Detective Griffin said.
As the student studies the dirt he was provided, which is now in different containers and bags, Detective Williams said the investigation gives the victim's family hope the deceased was not forgotten.
"They know something bad happened," Detective Williams said. "If you have knowledge of a homicide, you can be charged with concealment.
"The important thing is if you know about it, now is the time to come forward."