>>5548811 (lb)
DNA collection is easy and forget "Constitutional" protections, illegal immigrant or not.
Any bottle of water a person drinks from, and then discards, is fair game. Any cigarette smoked, and then put out, is fair game.
No search warrant necessary. Abandonment is consent for the government to collect. It's the same as a trash pull. Local agencies do it all day long, I guarantee the Feds do, too.