From the Document: "In July 2019, Attorney General William Barr instructed the Federal Bureau of Prisons (BOP) to take action to resume executions of inmates sentenced to death for violating federal law, ending an effective years-long moratorium. At the Attorney General's direction, BOP's then-Acting Director scheduled five federal inmates for execution in December 2019 and January 2020. A new addendum to BOP's execution protocol will govern the executions. That addendum provides for injection of a single drug, pentobarbital sodium, as the lethal agent. The BOP protocol previously called for application of a three-drug sequence, but the scarcity of the drugs involved and a review initiated by the previous Administration (as well as ongoing legal challenges) forestalled federal executions under the three-drug protocol after 2003."
CRS Legal Sidebar, LSB10357
Congressional Research Service: https://crsreports.congress.gov/