By Gary Robertson
RICHMOND, Va., Oct 1 (Reuters) - Lawyers for a Virginia serial killer asked a U.S. judge to halt his scheduled execution on Thursday, arguing that one of the drugs to be used might not work.
Attorneys for the inmate, Alfredo Prieto, 49, argued that pentobarbital, the first drug to be administered in the three-drug lethal injection, lacked a sterility test.
Prieto, a native of El Salvador convicted in two 1998 murders, is set to be executed at 9 p.m. EDT on Thursday (0100 GMT on Friday) at Greensville Correctional Center.
If the drug is faulty, "we believe it could him cause severe pain," attorney Elizabeth Peiffer told U.S. District Judge Henry Hudson. He said he would issue a decision on Thursday.
Hudson said during the hearing that pentobarbital had been used effectively 24 times in Texas executions. A compounding pharmacy produced the pentobarbital and Virginia obtained it from the Texas Department of Criminal Justice.
Prieto's lawyers had sought to halt the execution until the producer of the pentobarbital was named. They also sought guarantees of its potency and documents showing how it was stored and shipped.
The hearing had been scheduled to be held in federal court in Alexandria, Virginia, but was shifted to Richmond at the request of state officials.
Lawyers for the state contended in court filings that a certificate from Texas had guaranteed the drug's potency and that the drug was properly handled.
The hearing came as Oklahoma's attorney general sought to stay three executions in order to examine the cause of a mix-up with its lethal drugs.
Prieto was convicted in 2010 for the 1988 murders of Rachel Faver and her boyfriend Warren Fulton in Fairfax County, a Washington suburb. Faver had been raped.
Prieto was facing a 1992 death sentence in California for rape and murder when he was convicted in Virginia. Virginia officials say he has been convicted of killing or suspected of killing at least nine people.
Prieto's lawyers have sought a stay of execution from the U.S. Supreme Court. The stay would allow time for courts in California to rule on Prieto's claim that he is intellectually disabled.
They argue that Prieto has an IQ of 66 and is exempt from execution.
The execution would be the first in Virginia since January 2013. The state has carried out 110 executions since the U.S. Supreme Court reinstated the death penalty in 1976. (Writing by Ian Simpson; Editing by Mohammad Zargham and Eric Walsh)
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