A meth kingpin convicted of killing five people has become the third person this week to be executed by the US government.
Former Iowa chemistry student Dustin Honken, 52, was pronounced dead by lethal injection at 4.36 pm, according to the Bureau of Prisons.
Mr Honken's death sentence on Friday followed the executions of Daniel Lewis Lee and Wesley Purkey.
Lawyers, who were hoping for a last-minute reprieve, said Mr Honken was "redeemed" and had repented for his crimes.
"There was no reason for the government to kill him, in haste or at all. In any case, they failed. The Dustin Honken they wanted to kill is long gone," lawyer Shawn Nolan told the Associated Press.
"The man they killed today was a human being, who could have spent the rest of his days helping others and further redeeming himself. May he rest in peace."