A YOUNG IRAQ WAR VETERAN DIES IN A WRECK THAT LEFT HER EX-BOYFRIEND UNHURT - THE CRASH DIDN'T KILL HER, WHAT DID?

A WIFE'S SECRET RECORDINGS MAY HAVE THE ANSWER ON "48 HOURS: COLLISION COURSE"

On the surface, the death of Brittney Brashers seemed like an accident. The young woman, who was in the Air Force and served in Iraq, died while driving home with her ex-boyfriend, Robbie Walters. They had been drinking. She wasn't wearing a seatbelt; Walters was wearing his.

From the outset, police believed this was far more than just the tragic end to a night out, Susan Spencer reports in 48 HOURS: "Collision Course". How could she die in a crash that didn't seem severe enough to kill, while Robbie was uninjured?

Brittney's dad, Barry Brashers, had questions, too. He was at home in Illinois on Nov. 17, 2009 when he got the call from Denver police with news that his daughter was in a crash. "Talked to the doctor, and he told me she was no longer with us," Barry tells Spencer.

The Denver police were convinced they had a homicide on their hands and that Robbie was responsible, but had no way to prove it. Barry Brashers suspected Robbie as well. "She was dead because of him," Barry says. "To what extent, I had no idea what."

All along, Robbie maintained he was a passenger in the car and told police he didn't know what happened because he was falling asleep.

Robbie and Brittney had a tumultuous relationship. Brittney joined the Air Force looking for some direction in her life. She and Robbie met when they were both stationed in Iraq. He was married, though said the marriage was just to get more military pay. Robbie eventually was kicked out of the service for disciplinary problems. Brittney later returned home to the Air Force base in Colorado and back with Robbie, in spite of military brass telling her it was against the rules and that she needed to end the relationship. Eight months after they first met, an argument turned physical. Brittney ended up with bruises; Robbie ended up doing a few days in jail.

Brittney told friends she was in the process of breaking up with Robbie. She had joined a female football league and was going to a photo shoot for the team when Robbie begged to tag along to see her one last time. It was the last time, because driving home her car slammed into a parked car on a dead-end street.

"I'm staring at her and I'm yelling at her to breathe," Robbie tells Spencer. "I'm yelling at her to breathe, Brittney, breathe."

Investigators and the medical examiner were troubled by Brittney's death. "Here's this accident, I don't understand why this person's dead," medical examiner John Carver says.

Spencer and the 48 HOURS team piece together Brittney's last night alive through interviews with Robbie, Brittney's father, police, investigators and friends. Was it murder, or simply an accident? Working on a hunch, the lead detective got a major break in the case from Robbie's wife, who revealed secret recordings that would change everything.

48 HOURS: "Collision Course" will be broadcast Oct. 13 (10:00 PM, ET/PT) on the CBS Television Network. This broadcast is produced by Gail Zimmerman. Mike McHugh is the producer-editor. Al Briganti is the executive editor. Susan Zirinsky is the senior executive producer.

"Collision Course" is part of 48 HOURS' 25th full season. It's the third-longest running primetime series and has been the #1 non-sports program on Saturday nights for six consecutive seasons.

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