A Missouri appellate court has ruled that the state's prison officials aren't obligated to publicly reveal the source of the drug used to execute prisoners.

The appellate court's Western District decided Tuesday to overturn a 2016 trial court ruling that found the state wrongly withheld documents that would identify pharmaceutical suppliers, The Kansas City Star reported.       

The appeals court agreed with the state that a law that protects the identity of the state's execution team applies to those who supply the execution drug pentobarbital.

Major drug companies for the past several years have refused to allow their drugs to be used in executions. Missouri and many other active death penalty states refuse to disclose the source of their drugs, though the sources are widely believed to be compounding pharmacies ? organizations that make drugs tailored to the needs of a specific client. Those pharmacies do not face the same approval process or testing standards of larger pharmaceutical companies.

The appeals court ruling said that disclosing the identities of "individuals essential to the execution process" could hinder Missouri's ability to execute the condemned.

Several states also are facing legal challenges to lethal injection practices. Just last month, a federal judge found Ohio's latest lethal injection procedure unconstitutional while Texas sued the Food and Drug Administration over execution drugs that were confiscated in 2015. In Oklahoma last year, a grand jury criticized state officials charged with carrying out executions, describing a litany of failures and avoidable errors.