Justice Samuel Alito signed a brief order halting the execution Tuesday without giving any reason. But at 5:30 p.m. Wednesday, the high court removed the stay, 6 1/2 hours before the execution warrant expires, NBC News reported.
Smulls' attorney, Cheryl Pilate, said a stay from a lower court that was still in effect prevents the state from going through with the execution. NBC News said it was unclear whether Missouri would move forward with the execution Wednesday.
Smulls and Norman Brown were convicted of killing Stephen Honickman and wounding his wife Florence. The couple ran a small jewelry store in the St. Louis area where they showed gems by appointment, and investigators said Smulls and Brown posed as customers.
Brown is serving a life sentence with no parole.
Smulls' attorneys had been trying to halt the execution based on concerns about the chemicals used for lethal injection. Missourians for Alternatives to the Death Penalty accused the state of carrying out executions in "secrecy and haste."
"Though the state has granted anonymity to the pharmacy providing the lethal injection drug, it was recently revealed that the compounding pharmacy is located in Oklahoma and unlicensed in Missouri, making the lethal injection drug illegally obtained," the organization said on its website.