- Ruben Cantu, a high-schooler, was convicted of capital murder and sentenced to death
- After his execution, an investigative reporter uncovered evidence that he had been framed
- Then-District Attorney Sam Millsap has since changed his stance on the death penalty
"Death Row Stories" airs Sundays at 10 p.m. ET/PT.
(CNN)Sam Millsap Jr.'s resume reads like the start of a John Grisham novel.
In 1982, he became the youngest big-city district attorney in the nation, telling Texas Monthly a year later that it was the job he was "born and bred for."
"I was 35 years old and the smartest guy in the room," Millsap told CNN over the phone. "I was very proud of what I had achieved as DA."
After achieving a perfect record on capital murder cases in five years, he had every reason to be.
It wasn't until 2005, when Lise Olsen, an investigative reporter for the Houston Chronicle, asked to meet with Millsap that he ever doubted his spotless reputation.
A high-schooler on death row
For months, Olsen had been looking at the case of Ruben Cantu after a tip from one of her death penalty sources. In 1985, Cantu, a south San Antonio teenager, was convicted of capital murder for the death of Pedro Gomez.
"I was 20 years removed from the DA's office," Millsap said. "I hadn't given much thought to any specific cases in a long time."
Gomez, along with friend Juan Moreno, had each been shot nine times during a burglary at a home where they'd been working construction. The home's owner had asked the men to spend the night in the house to protect it against burglars who had recently stolen a water heater.
Gomez, who was shot in the head, died on the scene. Moreno survived and managed to call for help, but he would later lose a lung, kidney and part of his stomach because of his injuries.
Police never found the murder weapon and didn't gather any physical evidence from the scene. Millsap's prosecution was based on the eyewitness account of Moreno, who allegedly identified Cantu twice as Gomez's murderer -- once from a photo lineup and a second time during in-court testimony.
The jury convicted Cantu of capital murder after deliberating for just an hour and a half.
Four days after his conviction, Cantu wrote an impassioned letter to the residents of San Antonio saying he was "framed" in Gomez's murder case. Defense attorneys, who appealed Cantu's case multiple times, attacked police for coercing the only witness to the crime.
Their appeals were futile, and on August 24, 1993, Cantu was executed at the age of 26.
Dusting off a case file after a bar fight
While claims of innocence from convicted criminals are common, Olsen's research suggested that Cantu might have been speaking the truth in his letter.
Olsen's report, which came more than a dozen years after Cantu's execution, said that Gomez's murder had gone unsolved for four months with few leads. That's until Cantu had a run-in with an off-duty police officer at a nearby pool hall. The scuffle intensified, and Officer Joe De La Luz testified that Cantu, completely unprovoked, shot him four times. (His injuries were nonfatal.)
But Cantu was never prosecuted for that crime.
In her article, Olsen surmises that without enough evidence to indict Cantu in the bar shooting, officials instead began looking at him as a possible suspect in the Gomez murder.
She also uncovered that Moreno's eyewitness account was flawed. He had initially identified the suspects who shot him and Gomez inside the house only as "two Mexican teenagers." It wasn't until the third time police visited Moreno -- and after they said the name "Ruben Cantu" -- that Moreno identified Cantu in a photo lineup.
Moreno, who was an undocumented immigrant, later recanted his testimony against Cantu, saying he felt pressured by authorities to identify him.
'There is no victory in this story'
Millsap said his feelings about capital punishment had already started to shift before his first meeting with Olsen. In 2000, he went on record calling for a moratorium on the death penalty, saying he was "no longer convinced our legal system guarantees the protection of the innocent in capital murder cases."
But when he looked at Olsen's research, Millsap's opinion on the death penalty took a personal turn.
"It wasn't that I suddenly decided that Cantu was innocent," Millsap said. "But I was shocked."
Though the specifics are still a bit hazy, Millsap said his meeting with Olsen, and her article, "really threw (him) into a real funk."
"It never occurred to me that a case I had prosecuted would end up becoming one of the poster children for innocence in the death penalty debate," he said.
Eyewitness testimony, Millsap said, is not as reliable as he believed it to be when he was a young district attorney. If he had the opportunity to do it again, he said, he would not have sought the death penalty in the Cantu murder case.
Olsen's investigation garnered a great deal of attention and even led to a post-mortem investigation in 2007 by then-District Attorney Susan Reed. However, she found Cantu's conviction and execution to be justified.
For the last 10 years, Millsap has been an advocate for ending the death penalty, a stance that isn't always well received in a state like Texas, where more than 527 people have been executed in the past 40 years.
Millsap said it helps to use his own experiences as a motivator for change.
"It's not at all typical for a former elected prosecutor to acknowledge the possibility of imperfection," he said.
He also said he feels "a moral obligation to assume responsibility" for mistakes made in the Cantu case.
"This isn't about me," Millsap said. "It's beneath us as a people to permit such a system to exist."
Olsen, however, said she feels little vindication for her work.
"Ruben Cantu is dead," she said. "There is no victory in this story."