Ernest Johnson was put to death on Tuesday for using a hammer to kill three workers during a convenience store robbery in 1994.
Johnson, 61, died from an injection of pentobarbital at the state prison in Bonne Terre.
The Associated Press reported that Johnson silently mouthed words to relatives as the process began. His breathing became labored, he puffed out his cheeks, then swallowed hard. All movement stopped within seconds.