I believe it goes something like this:
1 star: A couple cop cars and bikes come after you.
2 stars: More cop cars and bikes come after you.
3 stars: Helicopters as well as the same amount of cop cars and bikes from 2 stars come after you.
4 stars: Those wagon things as well as more helicopters with lights and more cop cars and bikes come after you.
5 stars: All of the what I said above, plus FBI guys come after you.
6 stars: Some as above, just more and more of them.
After 5 stars though, unless you're max health and got armor, you're chances of surviving are almost slim to none. :/