HUNTSVILLE, Texas (AP) — A Texas inmate appeared headed for execution Thursday evening for the death of a prison guard after the U.S. Supreme Court refused to block the punishment.

Robert Pruett’s attorneys had asked the high court to review whether lower courts properly denied a federal civil rights lawsuit that sought additional DNA testing in the case. They also had questioned whether a prisoner who claims actual innocence, as Pruett does, can be put to death.

The justices, in brief orders and without comment, turned down the two appeals and requests for a reprieve about an hour before Pruett, 38, was scheduled to be taken to the death chamber.

Pruett was already serving a 99-year sentence for a neighbor’s killing when he was convicted in the December 1999 death of corrections officer Daniel Nagle at a prison southeast of San Antonio. Prosecutors have said the attack stemmed from a dispute over a peanut butter sandwich that Pruett wanted to take into a recreation yard against prison rules. Nagle was repeatedly stabbed with a tape-wrapped metal rod, though an autopsy showed he died from a heart attack that the assault caused.

Pruett would be the sixth prisoner put to death this year in Texas, which carries out the death penalty more than any other state. Texas executed seven inmates last year. Pruett would be the 20th inmate executed nationally this year, matching the U.S. total for all of 2016.

Pruett avoided execution in April 2015, when a state judge halted his punishment just hours before he could have been taken to the death chamber. His lawyers had convinced the judge that new DNA tests needed to be conducted on the steel rod used to stab the 37-year-old Nagle.

The new tests showed no DNA on the tape but uncovered DNA on the rod from an unknown female who authorities said likely handled the shank during the appeals process after the original tests in 2002.

In June, Pruett’s execution was rescheduled for October. Pruett’s attorneys then unsuccessfully sought more DNA testing and filed a federal civil rights lawsuit in August, arguing Pruett had been denied due process. The 5th U.S. Circuit Court of Appeals rejected the lawsuit last week, and Pruett’s attorneys appealed to the U.S. Supreme Court on Tuesday.

In a second appeal to the Supreme Court, also filed Tuesday, the attorneys asked justices to revisit the constitutionality of executing a prisoner who claims actual innocence in federal court because of newly discovered evidence after exhausting all other appeals. Supreme Court justices in 1993 ruled 6-3 in a Texas case that it was constitutional to do so.

Attorneys for Texas told the Supreme Court that Pruett’s appeals were intended to be a “further unjustifiable delay.” They argued the issues had been “repeatedly raised” and were previously “properly rejected” by the courts.

No physical evidence tied Pruett to Nagle’s death at the Texas Department of Criminal Justice’s McConnell Unit near Beeville. At his 2002 trial, prisoners testified that they saw Pruett attack Nagle or heard him talk about wanting to kill the guard. According to some of the testimony, he talked about possessing a weapon as well.

Pruett has said he was framed and that Nagle could have been killed by other inmates or corrupt officers at the McConnell Unit.

His trial lawyer, John Gilmore, recalled this week that Pruett had a horrible childhood environment and told of getting high with his parents when he was only 7 or 8.

Gilmore said he believed Pruett was going to be found not guilty of Nagle’s death. “But you’re defending somebody in prison already for murder. That’s already a big hurdle,” he said.

Pruett’s 99-year murder sentence was for participating with his father and a brother in the 1995 stabbing death of a 29-year-old neighbor, Raymond Yarbrough, at the man’s trailer home in Channelview, just east of Houston. Pruett was 15 when the attack happened.

According to court testimony from a sheriff’s detective, Pruett argued with Yarbrough and then got his father and brother to join him in attacking the man. Pruett punched and kicked Yarbrough and held him down while his father stabbed the man multiple times, the detective said.

Pruett’s father, Howard Pruett, is serving life in prison. His brother, Howard Pruett Jr., was sentenced to 40 years.

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