An Alabama inmate on death row survived a “botched execution” lasting 90 minutes as prison workers unsuccessfully searched for his veins, according to a federal lawsuit.

In late September, a knock on the window bordering the execution chamber ended the lethal injection attempt before Alan Miller was left alone for 20 minutes hanging vertically on a gurney with needle puncture wounds — wondering if he was to die that day, court documents state.

The event was described as “torture” after the U.S. Supreme Court allowed the execution to proceed.

Now attorneys representing Miller say he is “the only living execution survivor in the United States.”

Miller has awaited his execution after a judge sentenced him to death after two workplace shootings in 1999 that left three men dead in Alabama, according to the Montgomery Advertiser.

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A month before his execution date, Miller filed a complaint against John Q. Hamm, the commissioner of the Alabama Department of Corrections, Terry Raybon, the warden of Holman Correctional Facility in Atmore and state Attorney General Steve Marshall on Aug. 22, alleging he faced “constitutionally inadequate treatment” in prison, court records show.

Read more: Miami Herald