Solving Patty's murder seemed impossible - until Hamilton County prosecutors Mike Allen and Mark Peipmeier re-opened the investigation in 1999 with the hope that new DNA techniques might break the case.
"There's a chance that the killer also left his blood on here," Peipmeier said.
The prosecutors hoped to get DNA evidence from the clothing Patty and Mike wore that night.
"Obviously if we were able to get a link through DNA or some other blood evidence,...it would be a huge break in the case," Allen said.
But almost immediately, they ran into a roadblock. Over the years the evidence had been damaged in a flooded basement.
"I can only speculate as to why the DNA hasn't been preserved better than it has. But I think it probably has something to do with the flood," coroner Dr. Lee Parrot said.
Parrot tested the clothing but could not find any DNA. He could not at that point draw any further conclusions from studying and examining the evidence in terms of linking any suspect to the murder.
Even without DNA, prosecutors decided to present their case to the grand jury. They said they have witnesses coming forward for the first time who can help piece together the story of Patty's last night.
"So we feel we're building a strong circumstantial case," Allen said. "People's memories from 1963 are pretty good about this case; although granted, it's 37 years ago, a traumatic event like this, people remember."
And prosecutors have another angle: Wehrung has never fully accounted for his whereabouts at the time of Patty Rebholz's death.
"And at that time no one else is around," Peipmeier said. "It's hard to believe that someone else would have out of the blue done this....Someone did this pretty much in the heat of the moment, I would think, and it's someone that knew her, I'm convinced."
"It's my belief, yes, that she definitely knew her killer," Peipmeier said. "The circumstances point only to that."
In 2000, a grand jury indicted Mike Wehrung for Patty's murder. He was charged with second-degree murder.
The trial began last November.
Wehrung was found not guilty. The lack of DNA evidence may have played a part in the acquittal.
"Ultimately the reason the case was won is because the truth is Michael Wehrung didn't commit the crime. Juries generally do find the truth and this jury unquestionably found the truth.," said Wehrung's lawyer, Earle Maiman.
"When you place the fate of someone in the hands of a jury of 12, anything can take place," said Allen, the prosecutor. "While we certainly don't agree with the verdict of the jury, we accept it. That's our system. You accept it and you move on."
The truth of what happened to Patty Rebholz 39 years ago may never be discovered. But Mel Rebholz says that one day, someone will answer for his sister's murder.
"There's a higher court than Hamilton County out there and I truly believe that or I wouldn't have made it all of these years," he says.
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