Former small time methamphetamine dealer John Middleton, 54, was executed by lethal injection Wednesday for killing three people in rural northern Missouri in 1995, due to fear his victims would report his drug activities to authorities.

Middleton died after being injected with pentobarbital, marking the sixth execution in Missouri so far this year. The execution was initially scheduled for Wednesday at 12:01 a.m., but a federal judge granted a stay of execution late Tuesday, to allow time to assess if Middleton was mentally competent. The stay was overturned by a federal appeals court, and the U.S. Supreme Court and the Missouri Supreme Court wouldn’t halt the injection. Middleton’s claim that he is innocent and his request for clemency from Governor Jay Nixon were also denied.

U.S. Appeals Court lifts stay of execution for Missouri inmate: http://t.co/qeEDB3OHLn pic.twitter.com/lKCSQNxdi8

— Yahoo News (@YahooNews) July 16, 2014

#CNN : John Middleton Missouri Execution– His last words: "You are killing an innocent man."

— AnneClaire Stapleton (@AnneClaireCNN) July 17, 2014

After several drug suspects were arrested on June 10, 1995 in rural northern Missouri, Middleton allegedly told a friend, “The snitches around here are going to start going down.” He was eventually convicted of killing Randy “Happy” Hamilton and Stacey Hodge, and then Alfred Pinegar several days later.

Middleton and his girlfriend met Hamilton and Hodge on a gravel road, where Middleton shot and killed the two and placed their bodies in the trunk of Hamilton’s car. Fellow meth dealer Pinegar was shot in the face on June 23, 1995. Middleton left his body in a field near Bethany. Middleton then told acquaintances that he shot the three, and eyewitnesses saw him buying ammunition just hours before Pinegar’s death.

Middleton was convicted of triple homicide in 1997, and his girlfriend and accomplice, Maggie Hodges, is serving life in prison after pleading guilty to second-degree murder in all three deaths.

An anonymous criminal informant had said in February that Middleton accused him of being a snitch, and drove him out to see Pinegar’s corpse, and told him, “there’s already been three people killed. You want to be number four?” The witness signed an affidavit stating that he was then beaten unconscious with a baseball bat and his girlfriend was raped.

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