Michigan City, Indiana - The state of Indiana carried out its first execution in 15 years on Wednesday, putting to death a man suffering from mental illness who was convicted of murdering four people in 1997, including his own brother.

Joseph Corcoran (49) was executed by lethal injection and pronounced dead at 12:44 AM local time (0644 GMT) at the Indiana State Prison in Michigan City, officials said.

Asked whether he had any last words, he responded: "Not really. Let's get this over with," a statement by the Indiana Department of Correction said.

Corcoran's lawyers argued in court filings that putting him to death would violate the Constitution because he has long suffered from paranoid schizophrenia.

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They said that Corcoran experienced hallucinations and delusions, falsely believing that prison guards have been torturing him with an ultrasound machine.

Corcoran's "longstanding and documented mental illness continues to torment him as it did at the time of the 1997 offense," his legal team argued.

Last month, Corcoran sent a letter to the Indiana Supreme Court, saying he no longer wanted to litigate his case.

His lawyers nonetheless filed an emergency appeal to the US Supreme Court on Tuesday to stay the execution, which was ultimately rejected.

Corcoran was going through a stressful period in July 1997 because the upcoming marriage of his sister would see him moving out of the home he was sharing with her and his brother in Fort Wayne, Indiana.

After he overheard his 30-year-old brother James talking about him, he loaded his rifle and shot his brother and three other men, according to court filings.

Corcoran had previously been acquitted of the murders of his parents, who were found shot dead in their home in 1992.

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The execution was the 24th in the US this year. Three used the hugely controversial method of nitrogen gas, while the rest relied on lethal injections.

Indiana paused executions in 2009 because it was unable to obtain the necessary drugs, with pharmaceutical companies reluctant to be associated with capital punishment.

But Indiana Governor Eric Holcomb and Attorney General Todd Rokita, both Republicans, announced this summer that the state had acquired the drug – pentobarbital – and that executions would resume, beginning with Corcoran's.