“I just want to say I’m really sorry,” Billy Ray Irick said before he was put to death with a cocktail that includes Midazolam.
Nevada and Nebraska have both announced unprecedented plans to use fentanyl in executions.
Attorneys for Danny Bible, 66, proposed other execution methods that they say would be more humane for the elderly and sick prisoner.
Authorities said the man was behind a string of explosives set off or sent to people in 1989.
Russell Bucklew killed and raped. His lawyers argue that execution by injection could cause his tumors to burst and drown him in blood.
It is the latest in a series of dramatic efforts some officials have made to continue carrying out death sentences.
The decision comes nearly a month after the massacre that killed 17 people at a South Florida high school.
Eric Scott Branch was put to death Thursday for the 1993 rape and murder of 21-year-old Florida college student Susan Morris.
John David Battaglia killed his two children while their mother was on speaker phone.
The Justice Department said it would probably be seeking more federal death sentences in the months and years ahead.