The United States District Court for the Eastern District of Missouri has issued a stay of execution for John Winfield pending further notice.
Winfield had been scheduled for execution by lethal injection on June 18.
Winfield, 46, had applied for a stay following the botched execution of a condemned prisoner in Oklahoma in April. The United States Supreme Court granted a stay to Russell Bucklew in May based on that case.
Winfield had argued that his execution was unconstitutional since the drug used to perform executions in the state is unknown, and its maker is unknown.
In issuing the stay Thursday, the court also forbade the corrections department from "obstructing, pressuring, discouraging, or otherwise threatening any correctional employees from providing statements in support" of Winfield.
Winfield's attorney, John Luby, says that is the result of corrections officials intimidating an employee who spent a lot of time with Winfield and was willing to support his clemency petition by offering a positive character reference.
Winfield's lawyers claimed that that intimidation was a violation of Winfield's rights under the due process clause of the United States Constitution.
Winfield was convicted of killing two women in St. Louis County in 1996.