According to a report by the Houston Chronicle and the San Antonio Express-News, the police sergeant in charge of the investigation that led to the possible wrongful execution of Ruben Cantu in Texas had a record of wrongful arrests and was suspended three times for errors in judgment during his three decades with the San Antonio Police Department. Official documents examined by the papers revealed that Sergeant Bill Ewell, who supervised the homicide unit and was one of the driving forces behind the 1985 capital murder conviction of Cantu, participated in at least two documented faulty arrests during his years of service. Both of those cases involved Ewell's friend and colleague, officer Joe De La Luz, whom Cantu shot and wounded in a pool hall brawl in 1985. Though that incident was unrelated to the crime for which Cantu was ultimately executed, De La Luz's shooting resulted in Ewell's rekindled interest in Cantu as a suspect in an unsolved capital murder for which he was later convicted and executed.
The state's death penalty case against Cantu relied heavily on the testimony of the crime's only surviving eyewitness, Juan Moreno, a 19-year-old illegal immigrant. During initial questioning about the case, Moreno rejected Cantu's photo in a lineup of potential suspects. After Cantu shot De La Luz, Ewell ordered investigators to question Moreno a second and third time. Moreno now says that during the questioning he was pressured by police to identify Cantu as the murderer. His testimony during Cantu's trial was the only piece of evidence linking Cantu to the murder. Both Ewell and De La Luz also testified at Cantu's trial, but neither the jurors nor the attorneys heard about their friendship or about the dubious arrests they had made together. Sam Millsap, the former Bexar County district attorney who made the decision to seek the death penalty in the Cantu case, now says that he is troubled by the fact that Ewell and De La Luz's friendship went undisclosed during the trial. He notes that a close friend of De La Luz's should have had nothing to do with investigating Cantu in the pool hall shooting or the unrelated capital murder case.