Up until his death by lethal injection in the summer of 1993, San Antonian Ruben Cantu steadfastly claimed that he had been framed at the age of 17 for shooting two men during a robbery. One of them died, and the other lived to bear witness against him. An investigation of Cantu's conviction by the Chronicle's Lise Olsen provides persuasive evidence that his execution by the state was a mistake.

Opponents of capital punishment point to the fact that the Texas criminal justice system is far from fool-proof. Inevitably, they argue, death sentences will cause innocent people to suffer the ultimate, irreversible miscarriage of justice. The poor are at greatest risk of falling victim to a wrongful death sentence, as they must rely on an appointed lawyer who might not give the case his full attention. Every step of the way, from arrest to conviction to eventual execution, Cantu's history matches that scenario.

The 15-year-old who admitted participating in the crime, David Garza, has signed an affidavit claiming Cantu was not the gunman and was not at the scene of the shooting. Garza, incarcerated for an unrelated burglary, says both he and Cantu took a vow of secrecy not to identify the killer. He says he's speaking out now because he continues to be tormented by his failure to prevent the execution of his friend.

The surviving witness, Juan Moreno, testified at the trial that Cantu was the killer. Moreno claims police pressured him to ID Cantu after showing him Cantu's picture numerous times. He now says he is sure Cantu was not the man who shot him.

The individual Garza claims did the killing told police at the time that Cantu had confessed his role in the murder. There was no physical evidence tying the defendant to the crime. The jury did not believe Cantu's claim that he was in Waco stealing pickup trucks when the shooting took place, despite the fact that his sister corroborated the alibi.

Cantu's death sentence resulted in part from a later, unrelated incident in which he shot an armed off-duty police officer during a quarrel at a bar. That officer provided testimony that his shooting was unprovoked. Cantu claimed both had been drinking and he was defending himself. As the Chronicle investigation documented, the officer had previous suspensions for brawling in a bar and abusing a prisoner. Although he was never charged in that shooting, Cantu was arrested soon after and tried for the robbery-murder.

Cantu repeatedly asked his attorney to corroborate his alibi by finding several brothers who had been with him in Waco, but they were never located. The Chronicle tracked down one of them, who says that Cantu was not in San Antonio the night of the murder. Although Garza, Cantu's co-defendant, tried to alert Cantu's attorney that he was innocent before his execution, the lawyer never had time to visit him in jail to discuss the matter.

As the forewoman of the jury told a Chronicle reporter, the jurors did the best they could with the information they were given, but "the bottom line is an innocent person was put to death and we all have our finger in that." The district attorney at the time, Sam Millsap Jr., says he made a mistake trying Cantu for capital murder. Today's criminal justice system, he said, allows people to be convicted based on mistaken or corrupted evidence.

Jim Marcus is director of Texas Defender Services, which assists many Texas death row inmates in their appeals. He says the Cantu case shows the flaws in a system that frequently provides inadequate or incompetent counsel for capital murder defendants, both at their trials and during appeals. "When you have an airplane crash," Marcus said, "the FAA gets together and commits to an independent investigation to figure out where the failing was." He suggests a state commission should do the same for the capital punishment system in Texas.

University of Houston Law Center professor David Dow is the director of the Texas Innocence Network. He notes that Gov. Rick Perry has appointed a Criminal Justice Advisory Council, which has a subcommittee dealing with innocence issues. That group should thoroughly study the Cantu case.

Of approximately 160 Texas convictions overturned following DNA analysis, 70 percent of the wrongful prosecutions had relied solely on eyewitness identifications. "There isn't any reason to think the Cantu case is unique," Dow said.

Like Cantu, the next person to face execution in Texas, Tony Ford, also was convicted of murder on the basis of the accounts of two eyewitnesses, one of whom knew Ford was a suspect before making the identification.

The execution of one innocent person in Texas is too many at the hands of the state. The Chronicle's investigation of Ruben Cantu's life and death strongly argues for both his innocence and the need for new safeguards to prevent mistakes or malice from sending others to his fate.