The U.S. Supreme Court late on Thursday issued its second stay within hours in the death sentence of a former Eagle Scout condemned for a 1994 convenience store killing, apparently to consider a last-ditch appeal by his attorneys.

Ronald Smith, 45, had originally been set to die by lethal injection at 6 p.m. CST at the Holman Correctional Facility in Atmore, Alabama, before the Supreme Court ordered his execution put on hold with just hours to spare.

The court later lifted that stay, clearing the way for Smith's execution, only to reinstate the stay less than an hour later. The court offered no explanation for any the three orders it issued in the case on Thursday.

If Smith is put to death, he would be the 20th person executed this year in the United States and the second in Alabama, according to the nonprofit Death Penalty Information Center.

A month ago the Supreme Court had granted a last-minute hold to stop Alabama from carrying out another man's death sentence. Justices also did not give a reason for the stay of execution in that case.

Alabama's death penalty process is under scrutiny after the high court ruled in January that a similar death penalty law in Florida gave too much discretion to judges.

Smith was convicted of murdering Casey Wilson, a convenience store clerk in Huntsville, during a failed robbery.

The jury that convicted Smith recommended a sentence of life in prison without parole. But trial judge Lynwood Smith, now a federal judge, imposed a death sentence, as allowed by state law.

According to trial testimony, Smith had been an Eagle Scout and a member of the National Honor Society but struggled with alcoholism as an adult.

In an appeal to the U.S. Supreme Court, Smith's attorneys argued that his death sentence should be overturned.

They contended that Alabama's process was similar to Florida's, which the court struck down this year. The justices ruled that Florida judges were given powers that juries should wield in deciding eligibility for the death penalty.

The U.S. Supreme Court has since ordered Alabama to review similar practices in four other cases, not involving Smith, according to court documents. Those reviews are pending.

Alabama argues that its law is different from Florida's and that the Supreme Court ruling in the Florida case was not retroactive to earlier cases.

(Reporting by David Beasley in Atlanta; Additional reporting by Dan Whitcomb in Los Angeles; Editing by Jonathan Oatis and Leslie Adler)