DID A BROTHER AND SISTER CONSPIRE TO MURDER THEIR STEPFATHER? IN A CASE OF HE SAID SHE SAID, IT IS UP TO TWO JURIES IN ONE COURTROOM TO DECIDE IN AN EXCLUSIVE INTERVIEW THE SIBLINGS DISCUSS WHAT HAPPENED ON "48 HOURS MYSTERY," SATURDAY, MAY 16

On Thursday July 19th, 2007, the day after his 63rd birthday, Timothy MacNeil, a prominent defense attorney, was shot to death in his San Diego, Calif. home. The only witness was his 17-year-old stepdaughter, Brae Hansen, who was found tied up nearby. She told police a masked gunman had broken in and committed the murder, but left her alive.

Thinking Brae to be the victim of the crime, authorities looked to Brae as their best witness to help solve the case. But as she recounted the details of the murder to authorities and to her family, puzzling inconsistencies began to emerge, including the fact that she described the masked gunman by name - Nathan. Brae soon went from being a victim to being a suspect.

When questioned, Brae stunned the cops revealing details of a diabolical plot she said she and her brother Nathan had hatched to hire a hitman to kill their stepfather. Brae claimed that she changed her mind about committing the crime when the hitman didn't show up, but that Nathan went through with it himself.

"[I did] everything in my mind that I could think to stop it," Brae says in an exclusive interview with 48 HOURS MYSTERY. "I did think about calling the police once or twice and I had it dialed. I just couldn't push the send button. I was too afraid."

However, when Nathan was taken into custody, he said he wasn't even there, and that Brae was using him as a scapegoat to cover up the murder. "Personally I had more to gain from [Tim] being alive," Nathan says. "My sister had been angry [with Tim]...My sister probably went into a panic mode and automatically blamed me."

With brother and sister squarely pointing the finger at each other, prosecutors made the unusual and dramatic decision to try the siblings at the same time, in the same courtroom, but with two separate juries. Was the murder of Timothy MacNeil a crime concocted by two greedy siblings to kill their stepfather? Or, was one set up by the other? Who is telling the truth and who is lying?

Tracy Smith reports 48 HOURS MYSTERY: "Daddy's Girl" on Saturday, May 16, (10:00-11:00 PM, ET/PT) on the CBS Television Network. The broadcast is produced by Marcie Spencer, Gayane Keshisyan and Ira Sutow. Paul Ryan is the senior producer. Al Briganti is the executive editor. Susan Zirinsky is the executive producer.