Lawyers for 545 migrant children at the U.S.-Mexico border say they have been unable to locate the minors’ parents. The Department of Homeland Security has deported the parents of two-thirds of those children to Central America without reuniting them with their children, according to a court filing obtained by NBC News. In 2017, President Donald Trump’s administration ran a pilot program of its controversial 2018 family separation policy. The test run broke up roughly 1,000 families. An executive order ended the Trump administration’s “zero tolerance” border policy in 2019, and a federal judge ordered separated families reunited. Lee Gelernt, deputy director of the ACLU Immigrants’ Rights Project, told NBC News, “It is critical to find out as much as possible about who was responsible for this horrific practice while not losing sight of the fact that hundreds of families have still not been found and remain separated.”