Attorney General Eric Holder said Tuesday he personally opposed the death penalty and would support delaying all executions until the Supreme Court takes up whether lethal injection is constitutional.
In his latest remarks on capital punishment, Holder, the outgoing attorney general in President Barack Obama's administration, said seeing an innocent person executed by mistake was "the ultimate nightmare."
"Our justice system is the best in the world ... but there's always a possibility that mistakes will be made. For that reason I am opposed to the death penalty," Holder said.
He said it was appropriate for there to be a delay in place until the Supreme Court takes up the issue of lethal injection in April.
Several death row inmates recently have undergone apparent suffering during their executions using this method.
After the problems arose in the executions, Obama called on the Justice Department to review lethal injection executions.
"That review is still under way. Unfortunately, it won't be completed under my time as Attorney General," said Holder, who is stepping aside. Obama has nominated Loretta Lynch as his replacement.
Despite his misgivings about capital punishment, Holder sought the federal death penalty for the suspected perpetrator of the April 2013 Boston marathon attack.
It is "one thing to put somebody in jail for an extended period of time... (but) another" to execute them, with "no ability to correct a mistake," the attorney general said.
In 2008, the high court ruled that lethal injection was constitutional, and not a violation of the Eighth Amendment's ban on cruel and unusual punishment.
But since then, a majority of states have changed their drug protocols due to a shortage of the products used in the past.