Marcus Wellons
Death row inmate Marcus Wellons is seen in an undated handout from the Georgia Department of Corrections. Wellons is scheduled to die by injection on June 17, 2014 in what would be the first in the United States since a botched execution in Oklahoma in April ignited renewed debate and scrutiny of the death penalty. Reuters/Georgia Department of Corrections/Handout

Two death row inmates were executed by lethal injection within a span of two hours in the states of Georgia and Missouri, nearly two months after executions were halted in the country since a botched execution in Oklahoma fueled fresh debate about the death penalty in the U.S.

Marcus Wellons, who was convicted of the rape and murder of a 15-year-old girl, was executed Tuesday night and was declared dead at the Georgia Diagnostic and Classification Prison in Jackson, followed by the execution of John Winfield, who was convicted of killing two women and blinding another, early Wednesday morning in Bonne Terre, Mo. The executions came after the U.S. Supreme Court refused to grant a last-minute stay on the use of lethal injection.

The lawyers of the inmates, who had challenged the secrecy behind the nature, quality and source of the drugs used in the process, failed to block the executions.

The execution of the 59-year-old Georgia inmate was the first one after nine others were postponed nationwide since late April, when an Oklahoma death-row inmate died of a heart attack minutes after a doctor halted the execution after the procedure went awry.

According to reports, the drug used to execute Wellons was a pentobarbital, which the state had previously used in other executions, but had, for the first time, obtained it from "loosely regulated compounding pharmacies." John Ruthell Henry, another death row inmate in Florida, is reportedly scheduled to be executed on Wednesday night.

Unlike Oklahoma, which uses a cocktail of lethal drugs for the injection, Georgia and Missouri reportedly use a single drug, while Florida uses a three-drug combination of midazolam hydrochloride, vecuronium bromide and potassium chloride.

"I think after Clayton Lockett's execution everyone is going to be watching very closely," Deborah Denno, Fordham University School of Law professor and a death penalty expert, said of the botched Oklahoma execution, according to Associated Press. "The scrutiny is going to be even closer."

The execution of Lockett, which took place in late April, had been pending for several weeks as lawyers argued that the state withheld crucial information about the new cocktail of chemicals used for the lethal injection. The stay on his execution was later lifted by the Oklahoma Supreme Court, which ruled that the state had provided enough information regarding the injection to meet constitutional requirements.

However, during the execution, the drug reportedly did not work the way it was designed to, raising questions about the use of lethal injection cocktails, which have been blamed for causing undue suffering while violating constitutional protections against unusual and cruel punishments.