After nearly two decades, the federal government will once again begin executing criminals, the Justice Department announced Monday. Four inmates convicted of murdering children are set to be put to death by lethal injection.

"The four murderers whose executions are scheduled today have received full and fair proceedings under our Constitution and laws," said Attorney General William Barr in a statement. "We owe it to the victims of these horrific crimes, and to the families left behind, to carry forward the sentence imposed by our justice system."

The crimes were grisly. Daniel Lewis Lee murdered a family of three, including an 8-year-old girl. He's been on death row since 1999; his execution is scheduled for July 13. Wesley Ira Purkey, who raped and murdered a 16-year-old girl, will be put to death on July 15. Dustin Lee Honken, who shot and killed five people, will be executed July 17. Keith Dwayne Nelson, who kidnapped, raped and strangled a 10-year-old girl to death with a wire, will be executed Aug. 28.

Federal executions have been exceedingly rare in recent decades. According to the Death Penalty Information Center, only three have taken place since the federal death penalty was reinstated in 1988. All of those executions were carried out during the George W. Bush administration. One of those was Timothy McVeigh, sentenced to death for bombing the Oklahoma City federal building.