After 12 years without an execution, Arkansas had planned to carry out eight in 10 days, the biggest concentration in the United States in decades, because its supply of one of the drugs has an April 30 expiration date. Four of the executions were blocked by courts, and the timetable has drawn protests and intense criticism from death-penalty opponents, who cited the rushed schedule as evidence of the arbitrary way capital punishment is applied.

The last time a state carried out two capital sentences on the same day was when Texas did it, in August 2000, at a time when executions were more frequent in the United States.

What drove Arkansas’s accelerated schedule was that the state’s store of midazolam, one of the drugs used in its lethal injections, was set to expire, and states have had trouble acquiring new supplies.

Like several other states, Arkansas uses a three-drug combination in its lethal injections, but in recent years, drug companies have refused to sell their products for the purpose of executions. The first drug is midazolam, a sedative intended to render the inmate unconscious, though critics contend it is not always effective. The second drug is a paralytic to halt breathing, and the third stops the heart.