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The U.S. carried out its second federal execution this week by killing Wesley Ira Purkey on Thursday morning.

Purkey, 68, died by lethal injection at the Federal Correctional Complex in Terre Haute, Ind., at 8:19 a.m. local time.

The man was convicted in the 1998 kidnapping and killing of 16-year-old Jennifer Long, whose body was dismembered, burned and dumped in a septic pond. That same year, Purkey also was convicted in a state court in Kansas after using a claw hammer to kill an 80-year-old woman who had polio.

Purkey's lawyers contended he suffered from dementia and was unfit to be executed.

“I deeply regret the pain and suffering I caused to Jennifer’s family,” Purkey said in the moments before his execution. “I am deeply sorry. I deeply regret the pain I caused to my daughter, who I love so very much. This sanitized murder really does not serve no purpose whatsoever.”

In this 1998 photo, Wesley Ira Purkey, center, is escorted by police officers in Kansas City, Kan., after he was arrested in connection with the death of 80-year-old Mary Ruth Bales. (AP/The Kansas City Star)

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The U.S. Supreme Court cleared the way for his execution to take place just hours before, ruling in a 5-4 decision. The four liberal justices dissented — as they had in the first execution case earlier this week.

Justice Sonia Sotomayor wrote that “proceeding with Purkey’s execution now, despite the grave questions and factual findings regarding his mental competency, casts a shroud of constitutional doubt over the most irrevocable of injuries.” She was joined by Ruth Bader Ginsburg, Stephen Breyer, and Elena Kagan.

It was the federal government’s second execution after a 17-year hiatus. Another man, Daniel Lewis Lee, was put to death Tuesday after his eleventh-hour legal bids failed.

The federal prison in Terre Haute, Indiana, where Purkey was executed Thursday. (AP)

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Purkey’s lawyers had argued his condition had deteriorated so severely that he didn’t understand why he was being executed. They said he was repeatedly sexually assaulted as a child and had been diagnosed with schizophrenia, bipolar disorder, and other mental health conditions.

The issue of Purkey’s mental health arose in the run-up to his 2003 trial and when, after the verdict, jurors had to decide whether he should be put to death in the killing of Long in Kansas City, Missouri. Prosecutors said he raped and stabbed Long, dismembered her with a chainsaw, burned her body and dumped her ashes 200 miles away in a septic pond in Kansas.

Purkey was separately convicted and sentenced to life in the beating death of 80-year-old Mary Ruth Bales, of Kansas City, Kansas.

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Purkey had a long history of childhood trauma, was sexually abused by family members and a Catholic priest and was beaten by other family members, Liz Vartkessian, a mitigation specialist who worked with Purkey’s legal team and visited him dozens of times in the last five years, told the Associated Press.

But recently, Purkey’s mental health had seriously deteriorated to the point he didn’t have the stamina for long visits with his legal team and often forgot key facts and dates, she said.

Correction officers had to help him write down a schedule to remember his visits with his lawyers, Vartkessian added.

And he had a long history of paranoia and delusions and believed the Justice Department was moving forward with his execution because of many complaints and lawsuits he brought in prison, even though most had failed, Vartkessian said.

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The Supreme Court this week has also lifted a hold placed on other executions set for Friday and next month.

Dustin Honken, a drug kingpin from Iowa convicted of killing five people in a scheme to silence former dealers, is scheduled for execution Friday.

The Associated Press contributed to this report.