A FAMILY AND ITS BUSINESS PARTNER GUNNED DOWN AND A SUSPECT WITH AN AIRTIGHT ALIBI -- WILL AN OBSSESSED COP FINALLY CAPTURE A SUSPECT ON THE RUN FOR YEARS? "48 HOURS MYSTERY," SATURDAY, MARCH 3

In one day, the Dosso family lost their daughter, son, son-in-law, and trusted family business partner. They were shot execution style inside a manufacturing plant in central Florida on a late December afternoon in 1997. There were no fingerprints, DNA or weapons found at the scene. In time, there had come to be over 1,400 leads in the case, but a determined cop with the Florida Department of Law Enforcement became convinced of the guilt of one man very early on. Correspondent Harold Dow examines whether a cop driven by obsession pursued only one theory of the crime. And if a ruthless killer committed a multiple homicide and got away with it. 48 HOURS MYSTERY: "To Catch a Killer" will be broadcast Saturday, March 3 (10:00-11:00 PM, ET/PT) on the CBS Television Network.

"I became obsessed...I thought about it everyday," says special agent Tommy Ray. Not long after the killings, Ray became fixated on one suspect: Nelson Serrano.

Serrano was a likely suspect because he was a former partner in the lucrative business who was ousted when suspicion arose that he was embezzling from the company. The biggest problem with Ray's theory was that Serrano told law enforcement he was in Atlanta, at least 500 miles from the murder scene. He seemed to have an airtight alibi with an Atlanta hotel receipt and surveillance videotape tape from the hotel showing him standing in the lobby.

Ray's instincts, however, still kept him focused on Serrano. Ray tells 48 HOURS about a particular phone call he and Serrano had in which he showed no remorse about the brutal deaths of four people he knew. "He sounded like a killer," Ray says.

Ray, determined to get proof and justice for the distraught families, finally discovered Serrano's alibi was phony. He poured over hours and hours of that hotel videotape and realized the videotape that placed Serrano in the Atlanta hotel at 12:20 PM on the day of the murders does not have him reappearing in the lobby area until 10:17 PM - nearly 10 hours for which Serrano was unaccounted.

Did Serrano have time to fly to Orlando, pick up a rental car, drive to the scene and commit mass murder -- and then drive to Tampa, fly back to Atlanta and show up again on the hotel videotape? Oddly, Ray noticed that in both portions of the tape, Serrano, who claimed to have not left his hotel room due to a migraine he had all day, was wearing the same clothes.

Four long years after he hatched he theory, Ray finally got an indictment against Serrano. But the game wasn't over. The battle of wits was just getting started. The determined cop had a new, more daunting chase in front of him. Ray had to try to find a way to get Serrano, an indicted suspect thousands of miles away now living in a country with no extradition agreement with the United States, back home to face trial.

Ray accompanies 48 HOURS to Ecuador to help the questions: how can a Florida cop fly 2,000 miles to bring an indicted suspected killer to justice? And who would ultimately win -- the suspected killer or the cop who says he won't let him get away with four brutal murders?

48 HOURS MYSTERY: "To Catch a Killer" is produced by Steven Reiner and the field producer is Sara Ely Hulse. The senior producer is Peter Schweitzer. The executive editor is Al Briganti and the executive producer is Susan