As Nebraska prepares to complete its first state-sanctioned execution in two decades, human rights groups are condemning the death penalty and denouncing officials for operating under a “cloak of secrecy” in obtaining the drugs that will be used to kill Carey Dean Moore—substances that have caused tens of thousands of accidental deaths across the U.S. in recent years.

Amnesty International denounced the state’s move to participate in “the ultimate denial of human rights” after having carried out no executions since 1997.

“Rather than joining those states that have turned against this cruel and irrevocable punishment, Nebraska chooses to take a backward step that provides no constructive solutions to the challenges posed by violent crime,” said Kristina Roth, Amnesty’s senior program officer for criminal justice. “The U.S. capital justice system is fundamentally broken.”

After a federal appeals court rejected a pharmaceutical company’s attempt to block Moore’s execution, the nearly four-decade inmate will be put to death using a never-before-used combination of the opioid fentanyl, valium, a muscle relaxant, and a substance that will stop his heart—which anti-death penalty advocate Sister Helen Prejean denounced as “human experimentation.”

The German drug maker Fresenius Kabi has sued Nebraskan officials, accusing them of of illegally obtaining the substances, which the state is rushing to use before they expire.

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