We determined DHS law enforcement components did not consistently collect DNA from arrestees as required. Of the five DHS law enforcement components we reviewed that are subject to these DNA collection requirements, only Secret Service consistently collected DNA from arrestees. U.S. Immigration and Customs Enforcement (ICE) and the Federal Protective Service inconsistently collected DNA, and U.S. Customs and Border Protection (CBP) and the Transportation Security Administration (TSA) collected no DNA. DHS did not adequately oversee its law enforcement components to ensure they properly implemented DNA collection. Based on our analysis, we project the DHS law enforcement components we audited did not collect DNA for about 212,646, or 88 percent, of the 241,753 arrestees from fiscal years 2018 and 2019. Without all DHS arrestees’ DNA samples in the Federal Bureau of Investigation’s criminal database, law enforcement likely missed opportunities to receive investigative leads based on DNA matches. Additionally, DHS did not benefit from a unity of effort, such as sharing and leveraging processes, data collection, and best practices across components. We recommended DHS oversee and guide its law enforcement components to ensure they comply with collection requirements. DHS concurred with all four of our recommend.