Missouri carries out first known execution of an openly transgender person convicted of murder in 2003

Amber McLaughlin was executed this Tuesday in Missouri for a murder committed in 2003. (Credit: Jeremy S. Weis / AP)

(CNN) --

Missouri carried out the first known execution in the United States of an openly transgender person on Tuesday, when Amber McLaughlin, convicted of a 2003 murder and who unsuccessfully petitioned the governor for clemency, was put to death by lethal injection.

"McLaughlin was pronounced dead at 6:51 p.m.," the Missouri Department of Corrections said in a written statement.

"I'm sorry for what I did," McLaughlin wrote in his final statement, released by the Department of Corrections.

"I am a caring and attentive person."

• In which US states is there a death penalty and what crimes are punishable?

McLaughlin's execution – the first in the United States this year – is unusual: executions of women in the country are already rare.

Before McLaughlin's execution, only 17 had been sentenced to death since 1976, when the US Supreme Court reinstated the death penalty after a brief reprieve, according to the Death Penalty Information Center.

The nonprofit organization confirmed that McLaughlin is the first openly transgender person to be executed in the US.

McLaughlin, 49, and his lawyers had petitioned Republican Gov. Mike Parson for clemency, asking him to commute his death sentence.

Aside from the fact that a jury could not agree on the death penalty, they say, McLaughlin showed genuine remorse and has battled intellectual disability, mental health issues and a history of childhood trauma.

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But in a statement Tuesday, Parson's office announced that the execution would go ahead as scheduled.

The family and loved ones of his victim, Beverly Guenther, "deserve peace," the statement said.

"The State of Missouri will carry out McLaughlin's sentence in accordance with the Court's order," Parson said, "and dispense justice."

McLaughlin—listed in court documents as Scott McLaughlin—had not initiated a legal name change or transition and, as a death row inmate, was being held at Potosi Correctional Facility near San Luis, which housed male inmates, according to statements by McLaughlin's federal public defender, Larry Komp, and the governor's office.

McLaughlin had been convicted of murder and rape

McLaughlin was sentenced to death for the murder of Beverly Guenther in November 2003, according to court records.

The two were in a relationship, but had separated at the time of the murder and Guenther had received a protective order against McLaughlin after McLaughlin was arrested for burglarizing Guenther's home.

Several weeks later, while the order was in effect, McLaughlin waited for Guenther outside the victim's workplace, court records show.

McLaughlin repeatedly stabbed and raped Guenther, prosecutors argued at trial, pointing in part to blood spatters in the parking lot and on Guenther's truck.

A jury convicted McLaughlin of first-degree murder, forcible rape and armed criminal action, court records show.

But at the time of sentencing, the jury did not reach an agreement.

Most US death penalty states require a unanimous jury vote to recommend or impose capital punishment, but Missouri does not.

Under state law, in cases where a jury is unable to agree on the death penalty, the judge decides between life without parole or the death penalty.

The judge who tried McLaughlin imposed the death sentence.

If Governor Parson had granted clemency, McLaughlin's lawyers argued, he would not have undermined the will of the jury, since the jury could not agree on the death penalty.

However, that was just one of several reasons McLaughlin's lawyers said Parson should grant him clemency, according to the petition filed with the governor.

In addition to the jury deadlock issue, McLaughlin's attorneys pointed to his mental health issues, as well as a history of childhood trauma.

McLaughlin was "consistently diagnosed with borderline intellectual disability" and "universally diagnosed with brain damage as well as fetal alcohol syndrome," according to the petition.

McLaughlin was "abandoned" by her mother and placed into the adoption system, and in one placement she had "feces thrown in her face," according to the petition.

She later suffered further abuse and trauma, including being beaten by her adoptive father, according to the petition, and battled depression that led to "multiple suicide attempts."

At trial, McLaughlin's jury did not hear expert testimony about his mental state at the time of Guenther's murder, according to the petition.

That testimony, his lawyers said, could have tipped the balance toward a life sentence by supporting the mitigating factors cited by the defense and refuting the prosecution's assertion that McLaughlin acted with mental depravity—that his actions were particularly brutal or " basely meaningless"—the only aggravating factor the jury found.

In 2016, a federal judge vacated McLaughlin's death sentence due to the ineffectiveness of his attorney, court records show, citing the failure of his trial attorneys to present such expert testimony.

That ruling, however, was later overturned by the Eighth Circuit Court of Appeals.

McLaughlin's execution "would expose all the failings of the judicial system and would be a gross injustice on multiple levels," Komp, his attorney, told CNN.

"It would continue the systemic failures that existed throughout Amber's life, where there were no interventions to stop her and advocate to protect her as a child and adolescent," Komp said.

"Everything that could go wrong did go wrong for her."

CNN's Rebekah Riess and Emma Tucker contributed to this article.

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