(Adds background; federal judge denying stay of second execution slated for Thursday)
By Jon Herskovitz and Steve Barnes
April 18 (Reuters) - A major U.S. pharmaceutical firm sued Arkansas again over capital punishment on Tuesday, claiming prison officials fraudulently obtained a muscle relaxant to administer in several executions and demanding the drug in question be confiscated from the state.
Arkansas, which last carried out an execution a dozen years ago, has sought to resume capital punishment this month with a plan that originally called for putting eight inmates to death by lethal injection in 11 days.
That tally would have marked the highest concentration of executions over such a short period in a single state since the U.S. Supreme Court allowed reinstitution of capital punishment in 1976.
However, three of the condemned killers headed for the death chamber this month have already won stays of execution in a flurry of legal challenges and criticism that Arkansas was acting recklessly.
On Tuesday lawyers for all eight inmates filed a petition with the U.S. Supreme Court seeking a reprieve for the entire group on the basis of such issues as alleged flaws in the state's execution procedures and inadequate access to legal counsel.
Arkansas' death penalty push came as the number of U.S. executions fell to a quarter-century low in 2016. (For a graphic on the number and method of U.S. executions, see: http://tmsnrt.rs/26wAN2v)
Capital punishment in several states has been stymied by opposition of some global drug companies to the use of their products for executions and difficulties in finding effective replacements.
Arkansas contends it must act quickly because its supply of one of the drugs in its lethal injection mix, the valium-like sedative midazolam, expires at the end of April.
In a repeat of its lawsuit against Arkansas, McKesson Medical-Surgical, a unit of McKesson Corp, said the state's correction department had acted deceitfully when it purchased another drug, vecuronium bromide, a commonly used muscle relaxant given in extreme doses in executions to paralyze the body and halt breathing.
The state "intended to use this product in connection with executions, a fact that was never disclosed to McKesson," the company said in Tuesday's filing in state court in Little Rock.
McKesson originally sued Arkansas last week but withdrew the complaint after a federal court on Saturday temporarily blocked the 11-day plan for eight executions. But that ruling was overturned on Monday by a federal appeals court.
The company wants the drug supply in question impounded. Arkansas contends it has acted legally.
Five inmates remain in line for the death chamber in the coming days, starting with Stacey Johnson and Ledell Lee on Thursday in what would be the first dual executions carried out anywhere in the United States in 17 years.
On Tuesday, a state judge refused Lee's petition seeking a stay to allow for DNA tests his lawyers say would prove his innocence. A federal judge later denied a reprieve for Johnson, who asserted his obesity and other medical conditions posed the likelihood that death by lethal injection would subject him to unconstitutional pain and suffering.
(Reporting by Jon Herskovitz in Austin, Texas and Steve Barnes in Little Rock; Editing by Jonathan Oatis)