The US state of Arizona has revealed that a drug it uses for executions has been supplied by a UK company.
The admission came shortly before Jeffrey Landrigan was put to death after the Supreme Court lifted a federal judge's stay of execution.
The delay was based on objections that the drug was not US approved.
Arizona had to import the anaesthetic sodium thiopental after US supplies ran out. Concern has been raised in the UK, where there is no death penalty.
Arizona said it wanted to show the drug came from a "reputable place", in the first acknowledgement by a US state that sodium thiopental supplies come from outside the US.
'Business out of killing'
The shortage of supplies in the US had slowed executions since the spring.
Arizona's attorney general revealed that the drug had come from England but he did not name the supplier.
Writing in the Guardian newspaper, a British civil rights lawyer, Clive Stafford Smith, has called for the naming and shaming of the company as it was "making a business out of killing".
"One question that immediately springs to mind is whether it is criminal for the British corporation to profit from such a killing: while the language is loose, EU Council Regulation 1236/2005 takes a step along this path, making it illegal to trade in certain goods which could be used for capital punishment, torture, or other cruel, inhuman or degrading treatment...'
"When the veil of secrecy is inevitably sundered, this British corporation should be reminded that the medical profession boasts of a Hippocratic oath, not a hypocritical one," he wrote.
Landrigan, who is 50, was sentenced in 1989 for murder. He spent more than two decades on death row.
He was due to be executed on Tuesday morning, but the federal judge ordered a delay, calling for the source of the imported drug to be disclosed.
Landrigan's lawyers had argued that if the drug was obtained abroad it might not meet US drug standards and could fail to work properly.
Sodium thiopental is the first in a sequence of three drugs used in lethal injections.