Marta Hurtado, a spokesperson for the U.N. Office of the High Commissioner for Human Rights (OHCHR), said in statement that the agency is "deeply concerned" by Trump's December 22 pardon of former Blackwater guards Paul Slough, Evan Liberty, Dustin Heard, and Nicholas Slatten. The four men were sentenced to 12 years to life in prison for crimes including for first-degree murder for their roles in the September 16, 2007 Nisour Square massacre in central Baghdad.  "Pardoning them contributes to impunity and has the effect of emboldening others to commit such crimes in the future," Hurtado said of the Blackwater guards. 

"By investigating these crimes and completing legal proceedings, the U.S. complied with its obligations under international law," she added. "The U.N. Human Rights Office calls on the U.S. to renew its commitment to fighting impunity for gross human rights violations and serious violations of international humanitarian law, as well as to uphold its obligations to ensure accountability for such crimes."

In one of the most publicized crimes of the U.S.-led invasion and occupation of Iraq, Blackwater mercenaries were escorting a diplomatic convoy when, apparently unprovoked, they opened fire in the crowded square with machine guns, grenade launchers, and other weapons in broad daylight. 

"The shooting started like rain," recalled survivor Fareed Walid Hassan, who said he witnessed a woman dragging her dead young son as she fled for her life. Another victim, Mohassin Kadhim, was shot dead as she shielded her son in her arms.