Attorneys for the eight men attempted to block the executions, including using the argument that midazolam, the drug used to make inmates unconscious before two more drugs paralyze and kill them, does not effectively prevent a painful death.
Two minutes after Arkansas Department of Correction Director Wendy Kelley called for the execution to begin at 11:44pm, Lee's eyes began to slowly shut and he appeared to swallow multiple times before his eyes closed for the final time at 11:49pm.
"The department is prepared to carry out this sentence at this point", Solomon Graves, spokesman for the Department of Corrections, said less than 30 minutes before midnight.
A drugmaker asked Arkansas officials not to purchase its products for executions months before the state accepted a third-party "donation" of potassium chloride as one of three drugs to use in lethal injections, according to letters obtained by The Associated Press.
His execution was Arkansas' first since 2005. The first three executions were cancelled because of court decisions.
Gray's decision had effectively stayed all scheduled executions.
One of the drug companies was granted a restraining order after arguing in court that their drug wasn't supposed to be used for capital punishment.
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"What McKesson's lawsuit demonstrates is that the secrecy law is not created to protect the distributors and manufacturers; it's created to try to prevent them from learning that the state has improperly obtained the drugs", said Dunham, whose nonprofit group opposes the death penalty.
The pharmaceutical companies say there is a public health risk if their drugs are diverted for use in executions, and that the state's possession of the drugs violates rules within their distribution networks.
Gov. Asa Hutchinson's office acknowledged that the original plan confronted tall obstacles.
On Thursday night, Mr Gorsuch joined Chief Justice John Roberts and Justices Clarence Thomas, Anthony Kennedy, and Samuel Alito in denying Mr Lee's appeals and revoking the stay. Jack Jones and Marcel Williams are scheduled for execution on April 24 and Kenneth Williams is scheduled for execution April 27. Their prosecutors, their juries, local judges who oversaw their trials and, ultimately, the governor of this state believed them guilty. Williams is obese and diabetic. One of his lawyers has criticized the state for rushing through the execution before DNA testing that might have exonerated Lee could be done. The court's liberal wing-Justices Ginsburg, Breyer, Sotomayor, and Kagan-dissented, each voting to grant at least one of the stays. "In my view, that factor, when considered as a determining factor separating those who live from those who die, is close to random".
The second drug, pancuronium bromide, paralyzes the inmate.
However, last-minute court challenges have derailed three other executions scheduled for this week.
McKesson Corp., a drug company, has asserted that the state of Arkansas bought vecuronium bromide under false pretenses; McKesson does not sell the drug for executions.
The state's plan prompted an unprecedented flurry of legal filings and raised questions about US death chamber protocols and lethal injection drug mixes.