Diaz smiled and blew a kiss to several witnesses watching through a window, including his mother and grandmother.
He then turned to the father of his victim, watching through an adjacent window to the death chamber. "I hope this can bring some relief for you and your family," he told him.
He was pronounced dead 17 minutes later, at 6:30 p.m. CDT.
Texas Department of Criminal Justice officials have used pentobarbital as the single execution drug for more than a year, but Diaz became the first in the state given the sedative procured from a vendor or manufacturer the prison agency has declined to identify.
The expiration date of the department's existing inventory passed this month, possibly diluting its potency. Like other death penalty states, Texas officials needed to go to nontraditional sources because the usual suppliers bowed to pressure from capital punishment opponents and refused to make their product available.
In his appeal to the Supreme Court, rejected by lower state and federal courts, Diaz's attorney, James Terry Jr., argued recent high court rulings allowed another look at previously unsuccessful appeals where inmates had shoddy legal help. Diaz had deficient counsel at his 2000 trial in Hidalgo County and early in the appeals process, his attorney said.
Terry specifically questioned whether Diaz properly was advised of a plea offer from prosecutors before his capital murder trial, although court records show his trial judge questioned Diaz, who insisted on going to trial even with the possibility he'd get the death penalty. Terry also argued attorneys never reached out to Diaz's relatives to testify about how his unstable childhood contributed to his behavior, but records show Diaz's relatives wouldn't testify and Diaz didn't want them to testify.
In addition, Terry contended Diaz's initial appeals attorney was equally deficient for not addressing the trial lawyers' inadequacies.
Diaz, from Las Milpas, a small town between McAllen and the Mexican border, was convicted of the April 1999 slaying of Michael Nichols, 25, at Nichols' apartment in McAllen. Diaz also was given two life terms for attempted capital murder and aggravated robbery of another man who survived.
Cregg Thompson, the lead prosecutor at Diaz's murder trial, said evidence showed Diaz tried to steal Nichols' pickup truck but couldn't open a locked gate at the apartment complex. His shoe print was found on the keypad box at the gate, and his DNA was found on a beer bottle at Nichols' apartment.
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