WHEN A MOTHER IS MURDERED, A MYSTERIOUS WOMAN HOLDS ALL THE ANSWERS ON CBS NEWS "48 HOURS MYSTERY," SATURDAY, FEB. 6

In November 1994, the body of 33-year-old Farah Fratta was discovered in the garage of her Humble, Texas home. The mother of three had been shot twice in the head.

At the time of her death, Farah was in the midst of a divorce. To the outside world, Bob Fratta was an upstanding citizen, who worked in public safety as both a police officer and a fireman. But divorce documents were about to make his dark side public, revealing his strange sexual requests that not only embarrassed Farah, but also sickened her.

Bob Fratta seemed the likeliest suspect in his wife's murder. A few months before her death, Farah called 911 in a panic. A masked man had broken into her home through a window and attacked her. Farah suspected the intruder was a friend of her husband and authorities believed her, but had no concrete evidence. Now, in the wake of her death, investigators were sure of Bob's involvement again, but his alibi was hard to beat. Bob was at church with their three children as his wife was being murdered.

Investigators worked tirelessly to build their case against Bob and four months later they got an unexpected break. Tracing Bob's phone records from the night of Farah's murder led them to a mysterious woman who held all the answers to the case. But even more shocking than what she knew, was her startling admission: she could've prevented Farah Fratta's murder.

Click hereto watch a preview of Richard Schlesinger's report in 48 HOURS MYSTERY: "Thou Shalt Not Kill," to be broadcast on Saturday, Feb. 6 (10:00-11:00 PM, ET/PT) on the CBS Television Network. Click here for Schlesinger's reporter's notebook.

This broadcast is produced by Patti Aronofsky and Jenna Jackson. Judy Tygard is the senior producer. Al Briganti is the executive editor. Susan Zirinsky is the executive producer. 48 HOURS MYSTERY broadcasts are available on iTunes.