Willie Jerome Manning, at the Mississippi State Penitentiary at Parchman, Miss., is scheduled to die by lethal injection May 7. (AP)

Hours from execution, a Mississippi inmate renewed appeals Monday to retest DNA evidence in his conviction for the 1992 killings of two college students after the FBI acknowledged forensic errors in the case.

Lawyers for Willie Jerome Manning, 44, asked the Mississippi Supreme Court to stay his death by lethal injection, set for 6 p.m. Tuesday, after the FBI conceded over the weekend that one of its agents improperly claimed at Manning’s 1994 trial that hairs at the crime scene came from an African American. Manning is black; the victims were white.

As the high court considered Manning’s request for a stay, Gov. Phil Bryant (R) weighed a separate defense request to stay the execution filed after federal authorities acknowledged that the FBI agent exaggerated his ability to trace hairs to an individual.

The Justice Department and FBI offered to retest the DNA evidence, using new technology. Manning’s lawyers said a retest could determine whether another person was involved in sexually assaulting one of the two murder victims.

The new FBI admissions that an agent had erred in claiming he could identify hair from an African American injected a racial dimension to Manning’s final appeals, which had focused on whether advances in DNA testing could identify another or additional assailants.

Richard Dieter, executive director of the Death Penalty Information Center, said he could recall no instance in which federal authorities made statements favorable to a defendant or offered to retest evidence so late in a capital case, putting unusual pressure on state officials.

“Willie Manning is about to be put to death based in part on testimony that the FBI and the Department of Justice now admit was false,” David Voisin, one of Manning’s attorneys, said in a written statement. “Under these unprecedented circumstances, Mississippi officials cannot stand by and let this execution proceed.”

In a response to the court Monday, Mississippi Attorney General Jim Hood (D) called the FBI errors “merely a matter of semantics” because the agent at other points testified properly, and because the defense objected to the FBI’s testimony on different grounds at trial.

On Friday, Hood said the state was prepared to test “legitimate, exculpatory” DNA evidence, but called Manning’s claims dilatory and frivolous. Hood said the state court had ruled 5 to 4 last month that no new test results would exonerate Manning because of “conclusive, overwhelming evidence” of his guilt.

“He is the violent person who committed these heinous murders. May God have mercy on his soul,” Hood said Friday.

Manning was convicted of fatally shooting Jon Steckler and Tiffany Miller, who disappeared after a Mississippi State University fraternity party and whose bodies were discovered at a secluded spot outside Starkville, Miss., Dec. 11, 1992.

Manning was arrested after trying to sell some of Steckler’s belongings, including a compact disc player from his car. In addition, Manning’s cousin and a jail cellmate each said that Manning had confessed.

At Manning’s trial, FBI expert Chester E. Blythe testified that hair from an African American had been found in Miller’s car.

Late Saturday, John Crabb Jr., special counsel to the Justice Department, told lawyers in the case for the first time that Blythe’s testimony “exceeded the limits of the science.”

The FBI could only validly claim that a hair shared traits in common with a racial group, but could not place a probability on it, according to Crabb and a May 4 statement by the FBI laboratory.

On Thursday, Crabb notified the parties that Blythe also gave invalid, overstated testimony when he said he could match a crime-scene hair to an individual with “a relatively high degree of certainty.”

The Mississippi Supreme Court’s only black jurist, Associate Justice Leslie D. King, said in writing the minority dissent in Manning’s appeal that prosecutors emphasized Blythe’s testimony for prejudicial reasons, and improperly excluded potential black jurors.

“It is clear that the sole purpose in presenting the hair evidence was to have the jury conclude (1) hair from an African American was found in the car . . . (2) Manning is an African American, (3) therefore, Manning killed Miller and Steckler,” King wrote.

King also faulted prosecutors for excluding several black people from the jury.

In a separate dissent joined by the four judges, Associate Justice James W. Kitchens noted that state laws took effect only in 2009 that cleared the way for post-conviction DNA testing, recognizing advances in testing and expanded DNA and fingerprint offender databases.

Manning’s defense has cited several problems with his conviction, seeking the retest of a rape kit, fingernail scrapings, hairs and fingerprints. His lawyers also have noted that the jailhouse informant recanted his story, and that Manning’s cousin has given different accounts.

Manning was convicted and sentenced to death separately for killing two elderly women in their apartment in Starkville in 1993. That sentence remains on appeal.