Governor Jan Brewer of the southwestern U.S. state of Arizona has ordered an investigation after the execution Wednesday of a condemned inmate by lethal injection took nearly two hours.
Witnesses present at the execution of Joseph Wood said the convicted killer repeatedly gasped for air shortly after was injected with an overdose of a sedative and painkiller combination.
During the long interval, Wood's attorneys filed emergency appeals to state and federal courts to halt the execution, including the U.S. Supreme Court, saying it violated his constitutional rights against cruel and unusual punishment.
Justice Anthony Kennedy rejected the appeal, and Wood died before either a federal district court or the Arizona Supreme Court could hand down a decision.
Wood was sentenced to die for the 1989 shooting deaths of his estranged girlfriend and her father.
His attorney said Arizona has joined other states who have carried out "an entirely preventable horror - a bungled execution."
Two earlier botched executions this year have raised new questions about the process of lethal injection in the United States.
In January, a condemned inmate in Ohio gasped for breath for nearly 30 minutes after receiving a two drug combination identical to those used Wednesday in Arizona.
Then in April, a convicted killer in Oklahoma died of a heart attack after writhing in pain for several minutes because the drugs were not administered properly.
Wood's lawyers had filed court petitions to force Arizona officials to reveal details about the lethal injection procedure, the qualification of the executioner and the manufacturer of the drugs.
A U.S. federal appeals court had granted him a stay of execution last week, but it was overturned Tuesday by the U.S. Supreme Court.
The botched executions have led manufacturers to refuse to supply states with the drugs used in lethal executions. Several states have responded by by refusing to reveal details about the manufacturers.