From the Introduction: "Congress recognized that individuals without lawful immigration status may be particularly vulnerable to victimization and may be reluctant to help in the investigation or prosecution of criminal activity due to fear of removal from the United States. Through the Victims of Trafficking and Violence Prevention Act of 2000, Congress created specific immigration benefits, including U nonimmigrant status (also known as the 'U visa') for victims of certain crimes. [...] U.S. Citizenship and Immigration Services (USCIS) is the federal agency within the Department of Homeland Security (DHS) that adjudicates immigration and citizenship benefits, and has jurisdiction to determine who is eligible for a U visa. Law enforcement agencies assist USCIS by providing certifications on behalf of petitioners seeking U nonimmigrant status. The certification is a tool for law enforcement agencies to use as part of a victim-centered approach. [...] This Guide includes information about U visa requirements; the U visa law enforcement certification; best practices for certifying agencies and officials; answers to frequently asked questions from judges, prosecutors, law enforcement agencies, and other officials; additional resources; and contact information for DHS personnel on U visa issue."
U.S. Citizenship and Immigration Services: https://www.uscis.gov/