The drugs used in the botched lethal injection of Clayton Lockett "weren't working as they were designed to", a prison spokesman has said.
Jerry Massie told reporters:
"We believe that a vein was blown and the drugs weren't working as they were designed to. The director ordered a halt to the execution."
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European Parliament President Antonio Tajani had said "an extension of the transition period" had been discussed.
The film recreates the tragedy that killed 15 people an injured up to 700.
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