BOISE, Idaho (AP) — A U.S. appeals court panel on Friday declined to delay Idaho’s scheduled execution next week of one of the nation’s longest-serving death row inmates.

Thomas Creech was sentenced to death in 1983 for killing a fellow prison inmate, David Jensen, with a battery-filled sock. Creech, 73, had previously been convicted of four murders and was already serving life in prison when he killed Jensen.

He is also suspected of several other killings dating back half a century.

His attorneys had asked a 9th U.S. Circuit Court of Appeals panel in San Francisco to delay Creech’s death by lethal injection, set for Wednesday.

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They said they needed additional time to pursue a claim that, under the nation’s evolving standards of decency, his death sentence should be set aside because it was issued by a judge — not a jury. Among people on death row around the country, just 2.1% were sentenced to death by a judge alone, they said.

During oral arguments Thursday, the three judges expressed skepticism. They noted that while arguments about “evolving standards of decency” have been used to bar the execution of juveniles or people with severe developmental delays, Creech’s lawyers had presented little or no evidence that the people in the U.S. increasingly disfavor the execution of inmates who were sentenced by judges rather than juries.

“We gave you an opportunity to tell us what evidence you have of an evolving standard, and you haven’t provided anything,” Judge Jay Bybee told Jonah Horwitz, an attorney for Creech. “This feels like it’s a delay for delay’s sake and it’s a shot in the dark.”

The Idaho attorney general’s office opposed Creech’s request for a stay, arguing that Creech could have raised the issue long ago but waited until the last minute to try to forestall the execution: “This is a claim that was basically being held in the back pocket of Creech’s counsel, waiting until there was an actual execution that had been scheduled,” said Deputy Attorney General LaMont Anderson.

Creech’s attorneys in recent weeks have filed three other challenges regarding his execution. Two are with the U.S. District Court in Idaho, over the adequacy of his recent clemency hearing and over the state’s refusal to indicate where it obtained the drug it intends to use to kill him. The other is an appeal to the U.S. Supreme Court.

An Ohio native, Creech’s history of being involved in or suspected of murders dates back half a century. In 1974, he was acquitted in the stabbing death of 70-year-old retiree Paul Shrader in Tuscon, Arizona; Creech was a cook who lived at the motel where Shrader’s body was found.

He then moved to Portland, Oregon, where he worked as a maintenance worker or sexton at St. Mark’s Episcopal Church. The body of 22-year-old William Joseph Dean was found in Creech’s living quarters on Aug. 7, 1974, and a grocery store worker in Salem, Sandra Jane Ramsamooj, was shot to death that same day.

In November, Creech and his 17-year-old girlfriend were hitchhiking in Idaho when two traveling housepainters picked them up. The pair — John Wayne Bradford, 40, and Edward Thomas Arnold, 34 — were found shot to death and partially buried along a highway. Creech was convicted. His girlfriend testified against him.

During police interrogations, Creech made some far-fetched claims — claims that his attorneys say he made under the influence of so-called truth serum — that he had killed 42 people, some in satanic rituals and others in contract killings for motorcycle gangs in several states. Authorities were unable to corroborate most of his claims, but said they did find two bodies based on information he provided and they did tie him to nine killings: two in Nevada, two in Oregon, two in Idaho and one each in Wyoming, Arizona and California.

Authorities initially didn’t believe one of the stories that Creech told them. Creech claimed that while he was being treated at the Oregon State Hospital following a suicide attempt, he earned a weekend pass, traveled to Sacramento and killed someone, and then returned to the treatment center.

Based on that information, California police retested fingerprints found at the home of murder victim Vivian Grant Robinson — and they matched Creech. They also realized he had called the treatment center from her home to say he’d be returning a day late. Creech was convicted of that case in 1980.

During Creech’s clemency hearing last month, the state offered new information — without supporting evidence — that Creech had committed another killing in California, that of Daniel Walker in San Bernardino County in 1974. Prosecutors there say they do not intend to file charges, noting Creech’s upcoming execution.

Creech was initially sentenced to death following his 1975 Idaho conviction, but after the U.S. Supreme Court ruled that automatic death sentences were unconstitutional, it was converted to a life term. After killing Jensen he was again sentenced to death.