All of this is taking place under an ICE program called 287(g), part of a 1996 law that granted the Attorney General (and later the Secretary of Homeland Security) the authority to enter into written agreements with state and local governments on immigration. The first agreement under the law was signed by the Florida Department of Law Enforcement after 9/11; as of last year, the number of agreements has swelled past 1,000.
Today, the program employs a “task force model” under which local police are deputized as ICE agents with the authority to carry out federal immigration law. So despite the broad public backlash against ICE, the agency has a way to carry out its mission without drawing attention to itself.
An internal ICE diagram I obtained shows that local officers only become eligible for stipends and salary reimbursements after making their first arrest. The document labels that first arrest as the moment a participant becomes “OPERATIONAL.”