I think that the US Congress would do a good service to pass a law stating that if one is an illegal alien and does something like murder people in a DUI, they should get an enhancement of five years per life lost, no opportunity for parole, and the maximum sentence is imposed no ifs, ands, or buts. That won't, by itself, deter much in the way of illegal immigration, but it will serve as a qualified deterrent against those who are still here and pulling this crap. One of these illegals killed a family of NINE in Nashville a few years ago, and he got something like 36 months for vehicular homicide before he was sent back across the border to sit on the beach in Baja somewhere. That's just not right. He deserved to rot forever, and ideally should have gotten the needle, not a short stay in a county jail with relatively decent food and work release before he was driven to Ciudad Juarez and then walked right back across the border again.
Make it a straight-up law: if you commit a violent felony of any type in the United States as an illegal alien, then you will serve an enhanced prison sentence, and if you ever are found to be inside the U.S. borders again, it will be a death penalty offense, whether you have committed some other violent crime or not: your presence in the United States is a proximate threat to the country, and you need to be removed from the gene pool immediately. You've already demonstrated that you are a violent threat to Americans, so execution it is.
