Updated

An execution drug obtained by the Arkansas prison system earlier this month appears to have been made by a subsidiary of Pfizer, even though Pfizer has said it doesn't want its drugs to be used in executions.

The sale of the vecuronium bromide by an unknown third party may show how difficult it could be for manufacturers to prevent such sales in states like Arkansas that have execution secrecy laws.

The Associated Press on Monday obtained redacted photos of the vecuronium bromide label from the Arkansas Department of Correction. It matches labels submitted to the National Institutes of Health by Hospira, Inc., which Pfizer bought last year.

In May, Pfizer announced that it had put in place sweeping controls to make sure its distributors would not sell its drugs for use in executions.

A Pfizer spokeswoman said she'd comment on the matter later Monday.