This is very true. I have family in law enforcement, and the police in certain cities are simply not permitted to report these things. Nor, for example, could schools or hospitals report them, if they come into contact with such people.
One of the things I keep saying is that if you want to reduce illegal immigration, get after your very own local or state government, because they are the ones who are promoting measures that undo anything the Federal government could do. They make it easy and attractive for people to get in and stay and benefit.