The initial lawsuit, Glossip v. Gross, rose to the United States Supreme Court in 2015 at the preliminary injunction stage and involved an earlier version of Oklahoma's lethal injection protocol.

[1] In 2014, Oklahoma's lethal injection protocol came under scrutiny when Clayton Lockett died of a heart attack resulting from complications during his execution.

[3] In 2015, Lockett and other death row inmates had unsuccessfully challenged an Oklahoma law allowing the names of companies supplying drugs used in executions to be kept secret in Glossip v.

The lawsuit claimed that Oklahoma's execution protocol was unconstitutional, stating that there is autopsy evidence suggesting that the drugs used in lethal injection make people feel as though they are drowning through a "flash pulmonary edema" and like they are being "burned alive" violating the Eighth and Fourteenth amendments of the U.S.

[6] The lawsuit advanced to the United States Supreme Court, and on June 29, 2015, the justices ruled 5–4 in Glossip v. Gross that the prisoners had not shown that they would be subject to an unconstitutional level of pain.

[2][8] Scott Pruitt, Oklahoma Attorney General at the time, ordered a multicounty grand jury investigation of the execution drug error.

[2] Following the end of the moratorium, on February 27, 2020, more than two dozen inmates filed a Motion to Reopen Case by All Plaintiffs, claiming the new lethal injection protocol was incomplete.

[11][12] Although the case had been before the United States Supreme Court at the preliminary injunction stage, that had involved an earlier version of Oklahoma's lethal injection protocol.

[1] The plaintiffs claim the sedative midazolam, one of three drugs administered during Oklahoma's execution process, causes fluid to quickly build up in the lungs, creating a feeling of suffocation.

[5] They also claim that a second drug, potassium chloride, causes extreme pain "similar to being burned alive" if the person being executed maintains consciousness.

[5][11][15] An autopsy showed that John Grant suffered a flash pulmonary edema, which is a rapid build-up of fluid creating the feeling of suffocation or drowning.