Tens of thousands of migrants who illegally crossed into the United States from Mexico and were released into the country during President Joe Biden’s first year in office have disappeared and are untraceable, according to data from the Department of Homeland Security.

Nearly half, or 47,705, of the more than 100,000 noncitizens who were released from Border Patrol custody at the southern border in 2021 between March 21 and Aug. 31 and given instructions to self-report to Immigration and Customs Enforcement within 60 days have failed to check in, the DHS disclosed to Sen. Ron Johnson, a Wisconsin Republican.