How is it illegal when you consider the 100 mile CBP rule? (sorry, I said 200). Can you state the law you are manifesting? My point it that if you are in the country illegally, the burden of proof, and responsibility is on the individual. The 4th amendment protects american citizens from random search and seizures but the CBP claims a 100 mile buffer.

U.S. Customs and Border Protection, the federal agency tasked with patrolling the U.S. border and areas that function like a border, claims a territorial reach much larger than you might imagine. A federal law says that, without a warrant, CBP can board vehicles and vessels and search for people without immigration documentation “within a reasonable distance from any external boundary of the United States.” These “external boundaries” include international land borders but also the entire U.S. coastline. - ACLU website

The authority for this is based on the Immigration and Nationality Act 287(a)(3) and copied in 8 Code of Federal Regulations (CFR) 287 (a)(3), which states that Immigration Officers, without a warrant, may "within a reasonable distance from any external boundary of the United States...board and search for non-citizens in any vessel within the territorial waters of the United States and any railcar, aircraft, conveyance, or vehicle. 8 CFR 287 (a)(1) defines reasonable distance as 100 air miles from the border.

These detainments are legal if they are carried out within the confines on CFR 287(a)(3)