Did Texas execute the wrong man?

(CBS News) NEW YORK - In Texas, one question has haunted a family for years: Did the state execute the wrong man? This case raises serious questions that go to the heart of our legal system.

Rose Rhoton starts each day with a grueling eight-mile run. But that's nothing compared to the emotional challenge she's battled for the past 23 years -- trying to prove Texas executed an innocent man.

"If I would have known what I know now, he would have never been executed," she said.

The man was Rhoton's brother, Carlos DeLuna, who was put to death in 1989 for killing gas station clerk Wanda Lopez. Lopez's cries for help were captured on a 911 call to Corpus Christi police.

DeLuna was arrested near the crime scene and identified by a witness. He denied the killing, insisting it was another Carlos who had stabbed the woman.

Now, Columbia University law professor Jim Liebman says there was a second Carlos near the murder scene that night who looked strikingly like DeLuna. He was Carlos Hernandez, a man with a violent history and an obsession with the type of knife found at the crime scene.

"It was almost common knowledge in Corpus Christie that this named man Carlos Hernandez not only existed, but had taken the blame for killing Wanda Lopez," said Liebman.

Liebman and his students spent five years re-investigating the crime and have now published their proof of DeLuna's innocence.

One clue: the blood evidence. Crime scene photos show a blood-spatter 30 inches high, and the imprint of the killer's shoe.

Liebman claims police was sloppy. A photo shows a detective literally standing on the evidence, and another picture from the bloody crime scene reveals the imprint of the killer's shoe, an image that raises a troubling question.

"So he's leaving blood all over the place," said Liebman, "but there's no blood on DeLuna's shoe."

And Liebman found witnesses who strongly suspected Hernandez was the real killer. His former girlfriend Mary Margaret Tapia recognized the murder weapon. "This is Carlos Hernandez's knife," she said.

And then there's Janie Adrian, one of the friends who heard Hernandez boast about the killing. Asked what he said about Wanda Lopez, Adrian responded. "That he had stabbed her."

"We believe Texas has executed an innocent man," Liebman said. "We're certain beyond a reasonable doubt."

DNA evidence that might provide the final one percent, has been lost. The lead prosecutor told CBS News he stands by DeLuna's conviction, claiming Liebman selectively picked through the evidence to back his claim of DeLuna's innocence.

Rose Rhoton disagrees. "I need someone to say,'Hey you know what? We executed the wrong person. I'm sorry, I'm sorry.' That's all I ask for and take my brother out from being categorized as a killer.

But the one person who could clear DeLuna is gone. Ten years after DeLuna was executed, the other Carlos -- Carlos Hernandez -- died in prison.