Robert Roberson III had known for months he was scheduled to die Thursday afternoon. A lethal dose of pentobarbital would enter his veins sometime after the hour of 6 p.m., based on what an East Texas judge ordered this summer.

In addition to their appeal to Abbott, the defense filed a petition for a writ of certiorari to the Supreme Court of the United States. The petition urges the highest court in the nation to grant Roberson a stay of execution.

HOUSTON — The Texas Board of Pardons and Paroles on Wednesday denied a request for clemency for Robert Roberson, who could be the first person in the U.S. executed for a murder conviction tied to the diagnosis of shaken baby syndrome.