Cassandra “Casey” Williamson and Johnny A. Johnson.Photo: Getty Images; Missouri Department of Corrections via AP

Johnny Johnson and Cassandra “Casey” Williamson

A Missouri death row inmate was executed despite his attorneys' attempts to contest capital punishment on the grounds of his mental illness.

Johnson was convicted of the 2002 murder and attempted rape of 6-year-old Cassandra “Casey” Williamson in St. Louis County,PEOPLEpreviously reported, citing court records.

In astatementMonday, Missouri Gov. Mike Parson called Johnson’s crime “one of the most horrific murders that has come across my desk.”

“Casey was an innocent young girl who bravely fought Johnson until he took her life,” he wrote. “My office has received countless letters in the last few weeks seeking justice for Casey. Although this won’t bring her back, we hope that carrying out Johnson’s sentence according to the Court’s order may provide some closure for Casey’s loved ones.”

In 2005, a jury found Johnson guilty of numerous offenses, including first-degree murder, armed criminal action, kidnapping and attempted forcible rape. He was sentenced to death.

According to the AP, theKansas City Star,and St.Louis Post-Dispatch, Johnson expressed remorse in the moments before his execution.

“God Bless,” reads his final statement. “Sorry to the people and family I hurt.”

Johnson was executed following a failed bid to the U.S. Supreme Court seeking a stay of execution, according to the news outlets. Justice Sonia Sotomayor dissented, along with Justices Elena Kagan and Ketanji Brown Jackson.

However, Gov. Parson announced Monday that the execution would move forward after the Missouri Supreme Court ruled, and a federal appeals court upheld, that “Johnson was competent at the time and is competent now.”

The victim’s mother, Angie Wideman, told theSt. Louis Post-Dispatchlast week she was “ready to put the whole thing behind her.”

According to theDeath Penalty Information Center, Johnson’s death makes him the 16th prisoner to be executed in the U.S. this year.

In July 2002, then 24-year-old Johnson was staying at a friend’s house in Valley Park, where Casey and her father were also sleeping over, when the girl disappeared,records show.

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After the girl’s parents reported her missing, a search involving several law enforcement agencies was launched,FOX4 KCreported. The girl’s body was later found less than a mile from her home.

Johnson was quickly arrested and later confessed to the crime.

source: people.com