Dustin Lee Honken, who was convicted for the killing of five people, including a family of four that included two young children, was executed on Friday afternoon.
His final words were a prayer, "Mary Mother of God, pray for me," according to the reporter.
A federal judge declined to issue an injunction in Honken's execution. Lawyers for the inmate had requested that U.S. District Judge Tanya Chutkan issue a stay for the lethal injection.
Honken, 52, received the death penalty for the murders of two drug dealers who later became government informants, a girlfriend of one of those dealers, and her two children. Honken has maintained he is innocent over the years.
Prosecutors said he killed informants Greg Nicholson, and Terry DeGues, as well as Nicholson's 32-year-old girlfriend Lori Duncan and her two daughters, 10-year-old Kandi, and 6-year-old Amber.
A spokesperson with the Sisters of Providence said she was surprised at how calm Honken sounded over the phone in recent days, adding that his mother, brother, and daughter visited him.
It came after the Supreme Court cleared the Trump administration to carry out the first federal executions in the criminal justice system in nearly 20 years. Earlier in June, Attorney General William Barr ordered the Bureau of Prisons to implement the plan again.
He is one of several inmates on federal death row in the federal penitentiary in Terre Haute, Indiana, who have said the new one-drug protocol, which replaces a three-drug protocol the government last used in 2003, would cause an unnecessarily painful death.
Two other men convicted of murdering children were executed in Terre Haute earlier this week: Daniel Lee on Tuesday, and Wesley Purkey on Thursday.
While the Supreme Court’s conservative majority wrote that it had established that lethal injection was a constitutional method, some of the liberal justices complained that new problems raised by the changed protocol were being dismissed too hastily.