FOUR TEENAGE GIRLS MURDERED, TWO MURDER CONVICTIONS AND A CBS NEWS CORRESPONDENT'S CAREER-LONG DEDICATION TO A CASE THAT 18 YEARS LATER IS BLOWN WIDE OPEN ON "48 HOURS MYSTERY," SATURDAY, JAN. 9

Eighteen years ago, CBS News correspondent Erin Moriarty began reporting on what she says would turn out to be "the most horrific crime story I've ever encountered." In December 1991, four teenage girls were found murdered in an Austin, Texas yogurt shop. In a crime scene described by the lead detective as "wholesale carnage," the girls had been tied up, stripped down - at least one was raped - shot in the head and their naked bodies were stacked in a corner then set on fire.

In the weeks after the murders authorities received countless tips, many false confessions and even interrogated teenagers Maurice Pierce, Michael Scott, Robert Springsteen and Forrest Welborn after Pierce was caught with a gun at a local mall shortly after the crime. With no solid evidence they were let go.

Weeks became months and months turned into years with no developments in the investigation, until 1999, when the new detectives on the case made the stunning announcement that they made four arrests. More shocking was the news that it was the same four teenagers - now in their twenties - who police had spoken with eight years earlier. After being questioned by police this time, Michael Scott and Robert Springsteen confessed to the murders. Unable to crack Forrest Welborn, who claimed he didn't know anything about the crime, and with no evidence against Maurice Pierce, the charges against the two were dropped. Scott and Springsteen each stood trial for murder. Both were convicted with Springsteen condemned to death row and Scott sentenced to life in prison. But this case, full of unexpected twists, was far from over.

"I never thought that today, almost 18 years after these girls were murdered, that I'd still be reporting on this case," says Moriarty. In fact, the case that everyone thought was closed was about to be blown wide open.

"As a journalist, it has been difficult to watch both the victims' and suspects' families go through this wrenching legal process. And as a lawyer, it has been illuminating to witness the shortcomings of our legal system."

Click here to watch a preview of Erin Moriarty's report in 48 HOURS MYSTERY: "Innocence Lost," to be broadcast on Saturday, Jan. 9 (10:00-11:00 PM, ET/PT) on the CBS Television Network. Click here for Moriarty's reporter's notebook.

This broadcast is produced by Gail Abbott Zimmerman and Peter Henderson. Al Briganti is the executive editor. Susan Zirinsky is the executive producer. CBS News 48 HOURS MYSTERY broadcasts are available on iTunes.