Kenneth Fults, an intellectually disabled man who pleaded guilty to murdering his next-door neighbor in 1996, was put to death by lethal injection Tuesday night in Georgia.

Fults, 47, was pronounced dead at 7:37 p.m. at the Georgia Diagnostic and Classification near Jackson. He was executed with the state's single-drug lethal injection protocol, The Associated Press reported.

The U.S. Supreme Court hours earlier declined to stop Fults' execution over fairness issues raised by his lawyers, who cited racist comments made by a juror in his 1997 case. A day earlier, Georgia's parole board denied Fults' clemency petition based on his abusive upbringing and his intellectual disability.

Those troubling factors are typical of Georgia's use of the death penalty, said Amnesty International's senior death penalty campaigner, James Clark.

"Virtually every execution that’s happened in Georgia has been emblematic of problems with the death penalty," Clark said.

He noted that the 28 executions in the U.S. last year were carried out by just six states.

"In states like Georgia that are still carrying on a lot of executions, it’s because they’re not implementing issues of fairness," Clark said.

In the past several years, Georgia's death penalty -- which the law reserves for the worst of the worst -- has been given to a man with a strong claim of innocence, a man deemed intellectually disabled by every expert who evaluated him, and the lone woman on Georgia's death row whose jailhouse reformation helped save other inmates from suicide.

Fults, who was black, pleaded guilty to murdering his white next-door-neighbor Cathy Bounds during a burglary in 1996. He maintained he shot the 19-year-old woman five times in the back of the head by mistake while in a "dream-like state," according to court records.

With his guilty plea, jurors moved immediately to the second phase of his trial and sentenced him to death.

Juror Thomas Buffington later wrote in a sworn 2005 affidavit: “I don’t know if [Fults] ever killed anybody, but that nigger got just what should have happened. Once he pled guilty, I knew I would vote for the death penalty because that’s what that nigger deserved.”

During jury selection for the 1997 trial, Buffington, who is white, "explicitly denied harboring racial bias" and was seated on the panel. Buffington, who was 79 when he signed the affidavit, died in 2014. Lawyers noted in an April 8 court filing that two other jurors, in sworn affadavits, confirmed Buffington's statements and attitudes about race.

Fults' lawyers argued the Supreme Court should postpone the execution because the death sentence was tainted by racial bias. They cited the court's decision days earlier to hear a case from Colorado that involved a juror's racist remarks about the defendant.

The office of Georgia Attorney General Sam Olens argued that Fults raised the claim of juror bias too late.

The Georgia Parole Board was similarly unmoved Monday by testimony that Fults' trial counsel was ineffective and that he had suffered an abusive childhood. Several jurors quoted in Fults' clemency petition said his attorney was sleeping during proceedings.

"Throughout his life, Kenneth Fults was abandoned and rejected by those who were supposed to care for him, ridiculed and dismissed by those who could have helped him, and beaten up and down by family members and strangers alike," his lawyers wrote in his clemency petition.

The board also dismissed evidence of Fults' intellectual disability: He has an IQ of 74, which his lawyers said means he "functions in the lowest 1 percent of the population."

Clark said executing the intellectually disabled is the most common international human rights violation the U.S. commits with its death penalty. The country ranks fifth worldwide in the number of executions.

Georgia, Clark said, is an outlier among the 31 states with the death penalty.

The Supreme Court "has said it’s unconstitutional to execute someone with intellectual disabilities, but they’ve left it up to the state to determine who has one," Clark said. "Every state except Georgia uses a preponderance of the evidence” that includes tests for IQ and adaptive functioning.

"Georgia, uniquely, requires defendants to prove [intellectual disability] beyond a reasonable doubt,” Clark said.

Intellectual disability is by nature a subjective judgement and "is not something you can prove beyond a reasonable doubt," Clark said. Only one defendant in Georgia has ever met the legal threshold.