ATLANTA (Reuters) - Death penalty opponents urged Georgia on Monday to halt the execution of a man convicted of raping and killing a woman in 1994, saying there was inadequate evidence linking him to the crime.

Marcus Ray Johnson, 46, is scheduled to be executed by lethal injection on Wednesday for the killing of Angela Sizemore in Albany, Georgia. Sizemore, 34, was mutilated and stabbed 41 times with a small knife, according to trial testimony.

Amnesty International said "serious doubts" remained about Johnson's guilt, echoing concerns raised by supporters of Troy Davis, who was executed in Georgia on September 21 for the murder of a police officer.

"We are deeply troubled to see the state of Georgia prepare to execute another prisoner while serious doubts about his guilt are unresolved," said Laura Moye, director of Amnesty International's Death Penalty Abolition Campaign.

"Despite the enormous outpouring of concern from Georgians and those around the world about a deeply flawed system that ended Troy Davis' life, the state is gearing up to execute a person who may well be innocent."

The Davis case had attracted worldwide attention because of claims by his advocates he may have been innocent. No physical evidence linked Davis to the crime, and some witnesses changed or recanted their testimony after his conviction.

Prosecutors in Albany did not return phone calls for comment on the Johnson case but have stood by his conviction in comments to local media, saying there was nothing to indicate he was not the killer.

"There's no evidence that indicates that there was anybody else there, but even if there was anybody else there, like I said, none of it exonerates, nothing removes him from the crime," Dougherty District Attorney Greg Edwards said in remarks aired on local television channel WALB.

Trial testimony showed that Johnson met Sizemore in a bar in Albany. Sizemore had been drinking so heavily that the bar stopped serving her, a court synopsis of the case stated.

A bartender handed Johnson the keys to Sizemore's car, and the pair left together at about 2:30 a.m. A man walking his dog discovered Sizemore's body the next morning lying across the front seat of her car.

Johnson told police that Sizemore became angry because he did not want to "snuggle" after sex, and he punched her in the face. He said he "hit her hard" and then walked away. "I didn't kill her intentionally if I did kill her," he told police.

Citing Johnson's lawyers, Amnesty International said the case against Johnson was built on unreliable witness testimony from people who did not see the crime but had placed Johnson with the victim in the hours before the murder.

DNA testing matched blood on Johnson's shirt with Sizemore's blood, according to court records. But Amnesty, which campaigns against the death penalty, said there was a lack of physical evidence tying Johnson to the crime.

"Evidence of blood is not evidence of a commission of a crime, necessarily," Amnesty spokeswoman Suzanne Trimel said.

Johnson's lawyers asked the Georgia Board of Pardons and Paroles on Monday to grant their client clemency. A board spokesman said there would be no decision on Monday.

Defense attorneys have filed a motion for a new trial, calling for DNA testing on newly discovered evidence in the case. Lawyers for Johnson could not be reached for comment.

(Editing by Colleen Jenkins and Cynthia Johnston)

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