Christa Pike was still conscious and audibly snoring after receiving the drugs, according to her legal team, which filed two emergency submissions in federal and state court to halt the execution and ensure she received medical care.
Media witnesses described Pike as somewhat alert, and at one point she sang with her spiritual adviser. Reporters said curtains around the execution chamber remained closed for nearly an hour, during which they could hear breathing and steady snoring. Emergency vehicles arrived at the prison shortly after witnesses were escorted out and departed about 15 minutes later.
It was not immediately clear what went wrong with the administration of pentobarbital, the lethal drug used. The state had raced to carry out the execution before the day ended to avoid having to reschedule, after a lengthy legal limbo pushed proceedings deep into the night.
The apparent failure is likely to renew scrutiny of lethal injection procedures in Tennessee and across the United States.