Convicted serial killer Joseph Paul Franklin was executed at 6:17 am. Controversy surrounded the details of his execution.
"We will continue to pray for all of those people who were victims of Mr. Franklin's and we continue to pray for him too," Father Friedel of St. Peter the Apostle Church said.
Missouri recently changed the number of drugs used for lethal injection from three to one.
"The concern is the first drug masks the kind of pain that the subsequent drugs put the person they are executing through," Missouri Western Professor David Tushaus said.
Franklin is the first inmate executed by Missouri in more than two years, but his execution is one of a long line of capital punishment in the state.
Missouri ranks fifth among the states that allow it, in the execution of convicts.
Texas has executed far more than any other state with more than 500.
Missouri is also one of the only states that legally allows the gas chamber as a form of execution. While they have never used it, the option is available as an alternative.
Eighteen states and the District of Columbia have all abolished the death penalty.