BONNE TERRE, Mo. — A former methamphetamine dealer was executed Wednesday for killing three people in remote northern Missouri out of fear that they would report his drug activity to police.John Middleton, 54, died Wednesday night from an injection of pentobarbital, the sixth execution in Missouri this year. Only Florida and Texas, with seven each, have performed more executions.Middleton was convicted of killing Randy "Happy" Hamilton and Stacey Hodge in early June 1995, then Alfred Pinegar several days later. He maintained to the end that someone else was responsible for the slayings."You are killing an innocent man," Middleton said in his final statement.State officials, including Gov. Jay Nixon, disagreed."Tonight has brought a conclusion to a case that illustrates how methamphetamine can have such a monstrous impact on so many lives," Nixon said in a statement.Michael Black, Pinegar's uncle, questioned why it took so long for the execution to occur."Nineteen years seems like a long time to wait for justice," he said following the execution.Middleton was a small-time meth dealer in sparsely populated northern Missouri in the mid-1990s. After several drug suspects were arrested on June 10, 1995, he allegedly told a friend: "The snitches around here are going to start going down."A day later, according to court records, Middleton and his girlfriend met Hamilton and Hodge on a gravel road. Prosecutors said Middleton shot and killed them both and hid the bodies in the trunk of Hamilton's car.Pinegar, another meth dealer according to police, was shot in the face on June 23, 1995. His body was found in a field near Bethany.Acquaintances say Middleton told them he killed all three. Police also had eyewitness accounts of Middleton purchasing ammunition in the hours before Pinegar's death. Middleton was convicted in 1997.Middleton's girlfriend, Maggie Hodges, is serving life in prison after pleading guilty to second-degree murder in all three deaths.In February, a man whose name has not been disclosed because he fears retribution signed an affidavit saying that two rival meth dealers drove him to a rural area soon after Pinegar's death and accused him of being a snitch. He said the men showed him Pinegar's body, saying: "There's already been three people killed. You want to be number four?"The witness said the two dealers then beat him unconscious with a baseball bat and raped his girlfriend.Neither police nor the courts were swayed by the new witness. Harrison County Sheriff Josh Eckerson agreed to take a new look at the case but said his investigation found no evidence to back up the claims. He is convinced that Middleton was the real killer. Several court appeals claiming innocence were turned away.Concerns about whether Middleton was mentally fit for execution, though, spurred a long delay in the execution, which occurred 19 hours after it was originally scheduled, at 12:01 a.m.A federal judge granted a stay of execution late Tuesday, citing a need for a hearing to determine if Middleton was mentally ill. Courts have held it is unconstitutional to execute the mentally ill.A federal appeals court overturned the stay later Wednesday and neither the U.S. Supreme Court nor the Missouri Supreme Court would halt the execution.Missouri has executed one man each month since November, with the exception of May, when the U.S. Supreme Court halted the execution of Russell Bucklew. Bucklew suffers from a rare congenital condition that causes weakened and malformed blood vessels as well as tumors in his nose and throat. The 8th U.S. Circuit Court of Appeals plans a hearing on Sept. 9 to determine if lethal injection could cause him to suffer because of his medical condition.Another execution is scheduled for Aug. 6, when Michael Shane Worthington is scheduled to be put to death for the rape and killing of a suburban St. Louis neighbor in 1995.