There was someone with a motive for murder. But that day he was 500 miles away.

So the crime remained unsolved, until one investigator who would not rest slowly started to unravel the mystery.

It took nearly a decade, but finally one tiny piece of evidence blew the case wide-open: Would it be enough to catch the killer?

Dateline Correspondent Dennis Murphy closes the book... on "Unfinished Business."

Dennis Murphy gives us a preview in this blog entry:

"Tommy Ray and he works for the Florida Department of Law Enforcement— the F.D.L.E., which is like the state's version of the F.B.I., supercops who get called in on the big cases. In 1997, Tommy was put in charge of the investigation into an awful crime. Someone, or maybe more than one, had cooly walked into a family-owned manufacturing business and gunned down four people execution-style— three men and a woman— in the offices just off the shop floor where they made garment conveying tracks like you see at your dry cleaner. Four families were devastated and united in their belief that a recently-ousted business partner had been the shooter or had paid someone to do it. After digging into the history of bad blood at the plant— allegations of stealing, threats— Agent Tommy Ray came to believe the family was right. The fired business partner, a man named Nelson Serrano, had been the architect of the quadruple homicide. 'I know he was definitely involved,' the detective told us, 'I just wasn't sure how he pulled it off.'" Click here to read more.

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