Sometimes, after a defendant has been arrested for a crime, an Immigration and Customs Enforcement (ICE) officer will file an immigration detainer with the agency that has custody of the defendant. The detainer asks the agency to notify ICE when the defendant would otherwise be eligible for release — for example, because the defendant has posted bond, or because the charges against the defendant have been dismissed — and to hold the defendant for up to 48 hours thereafter to enable ICE to take custody of the defendant. I have often wondered about the authority for holding a defendant pursuant to such a detainer. Recent developments indicate that courts are increasingly wondering about that too.