It's been three years since Christian Olsen was sentenced to death for killing Etta Jean Westbrook, who lived across the street from him in Bryan. Tuesday, that sentence was over-turned and it all hinged on one witness for the defense in the punishment phase of Olsen's trial.

In less than an hour, a jury found Christian Olsen guilty in February 2009. About two weeks later, he headed to death row, but an appeals court ruling will have him coming off.

"We don't like to make these kind of mistakes," Brazos County District Attorney Bill Turner. "We don't like for our office to make those kind of mistakes. In capital cases, they're very strictly scrutinized, and we understand the reason."

Olsen's defense argued that his girlfriend, Kelly Sifuentez, had a huge negative influence on the then-20-year-old, and that he shouldn't die because of it. In fact, the two had been charged in the murder of Sifuentez's mother six months earlier. Sifuentez was later sentenced, while prosecutors didn't pursue a trial for Olsen since he was already on death row.

Defense attorney Billy Carter planned on calling Texas State associate professor Donna Vandiver to help show Sifuentez's influence..

"Ever since that relationship began, Christian Olsen's behavior -- everything he'd been doing in his life -- began spiraling downward," Carter said.

But the prosecution argued Vandiver wasn't qualified to interpret Olsen's psychological or psychiatric records,which she admitted. The defense was going to argue that his girlfriend was a sex offender -- grooming him, manipulating him -- and prosecutors said there wasn't evidence to show that.

The defense said Vandiver was only going to answer hypothetical questions and testify whether Kelly Sifuentez's actions were consistent with sex offenders, a focus of her research.

Judge Steve Smith sided with the prosecution, and the jury never heard Vandiver.

But the Texas Court of Criminal Appeals ruled "...the trial judge abused his discretion by excluding Dr. Vandiver's testimony." It ruled "...the jury was unable to fully comprehend the mitigating potential of the evidence that was before it," and said "...(Olsen) was unable to explain or rebut the State's" argument that he could be a future danger.

"I was shocked we couldn't present her," Carter said. "She was our most critical witness. As I look back on it, she was the real witness we wanted the jury to hear."

We asked the trial's prosecutor, Shane Phelps, whether he'd make the same argument against Vandiver if given the chance again.

"Given the way the questioning was, I'd probably make the same decision," he said. "From the perspective now, thinking about the family having to go through this again, I wish we had let her talk to the jury, because I don't know if the result would have been any different."

Turner's office will decide whether to retry the punishment phase and seek the death penalty after reviewing things and consulting with Westbrook's family. Otherwise, Christian Olsen would serve life in prison without parole.

According to TDCJ, Olsen remains on death row until a decision is made by Turner. If they go after the death penalty again, he'd be returned to Brazos County until trial.