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KANSAS CITY, Mo. — Advocates for a Missouri inmate held a vigil in Kansas City on Tuesday, hours before he was set to be executed.

The group, along with Missourians for Alternatives to the Death Penalty, were hoping the U.S. Supreme Court would stop the execution of Ernest Johnson. But minutes after the vigil started, supporters learned the court had declined to stop the execution.

He was scheduled for execution Tuesday evening at the state prison in Bonne Terre, about 50 miles south of St. Louis. It would be the seventh U.S. execution this year.

The 61-year-old was convicted and has admitted he killed three victims at a Casey’s convenience store in Columbia, Missouri, in 1994.

Johnson’s lawyer Jeremy Weis said he suffers from a mental illness and has a low IQ, essentially the intellect of a child. Weis argues executing Johnson would violate the Eighth Amendment to the U.S. Constitution, which prohibits executing intellectually disabled people.

“No one is trying to take away from the crime that he committed,” said Latahra Smith, volunteer with MADP. “I was a pretty hideous crime, but I don’t think us saying, ‘Don’t execute him and give him prison, life in prison with parole,’ I don’t think that’s minimizing anything.”

Supporters with MADP said this was a scheduled vigil because Gov. Mike Parson did not grant clemency for the death row inmate.

“Mr. Johnson is intellectually disabled and has been,” Smith said. “This is notated in his medical records going back to a child, and I think that’s really sad when our 8th Amendment says that we’re not clearly supposed to be doing this.”