Author dedicated to seeking justice in "sweetheart murders" case

(CBS) To the families of murder victims John Riggins and Sabrina Gonsalves, journalist and author Joel Davis is an unsung hero. They credit his investigative work with putting pressure on the criminal justice system to close this case.

Davis has dedicated years to this murder mystery - despite some overwhelming obstacles.

"These are my files on the case and I have them in alphabetical order for the most part," Davis explained during an interview with"48 Hours". "...we have affidavits, we have defense attorneys and various other theories ..."

The abundant -- if somewhat messy -- files in his office tell the story of Davis' 12-year dedication to this case.

"I've had people say, you know, 'you're obsessed, you're obsessed with this,'" he explained. "No, I'm not obsessed. I just did my job."

Davis, who is now 50, attended high school in Davis, Calif., with John Riggins. In 2000, he decided to write a book about the so-called "sweetheart murders."

Asked what it was about this case that captured his imagination, Davis told "48 Hours" correspondent Troy Roberts, "Well, having grown up here ... it just had a seismic impact on the community."

"How did the murders change the town of Davis?" Roberts asked.

"I think, like any small town, I know there was a lot of fear," Davis replied. "I think it left kind of an indelible imprint, because in my estimation ... it's probably the most shocking crime in the history of the city."

Davis admits he rattled some cages as he sought answers to why the case hadn't been closed. "It just sort of bothered me that it was unresolved after all these years," he said.

He persisted even as he battled a devastating diagnosis: at the age of 38, he was told he had Parkinson's disease. "48 Hours" talked to him about it back in 2006.

"When you have Parkinson's you gotta say the glass is half full, that's the way you survive it. It's a disease that - as Michael J. Fox likes to say, he calls it 'the gift that always takes.'" Davis got emotional as he continued: "I've had my ability to walk taken away ... I've had my ability to sign a check taken away but I can still write."

Thanks to modern medicine, Davis can still control his hands enough to use a computer. He's undergone two deep brain stimulation surgeries. And though it's tough to walk, he made it to court through years of drawn-out proceedings. He plans to update his book.

"Why do you think people were still fascinated with this case after 32 years?" Roberts asked.

"I think it's kind of a classic good versus evil story," Davis replies. "It also plays into that CSI, DNA who- done-it classic sort of mystery."

But while DNA and an experienced team of investigators ultimately closed this case, the father of murder victim John Riggins believes Davis' efforts also played a role.

"I'd like to thank Joel Davis and his book, 'Justice Waits'," Dr. Richard Riggins testified. "He really kept this flame of justice alive when it was about to go out."

"When Dr. Riggins acknowledged you in court, it was an emotional moment for you," Roberts noted.

"Yeah ... the fact that he was kind enough to acknowledge me on the witness stand really made me feel good," said Davis. "I do think that the pot needed to be stirred and that the case needed to be held up to the light."