This is from only one county, but I found these numbers (check out the table) instructive:
About 2 percent of the people charged with major violent crimes in
Prince William County last year were illegal immigrants, but they were
arrested for a larger portion of secondary offenses, according to newly
released statistics and a Washington Post analysis that offer the first
comprehensive look at criminal activity since the county implemented
its controversial anti-illegal immigration measures.
The crime of prostitution has the highest percentage of illegal immigrants as arrestees, namely 21.4 percent. If you are wondering, the new county procedure is to check the immigration status of everyone taken into custody. A few points:
1. Immigration has worked much better in northern Virginia than in many other parts of the country, most of all southern California. The number will not be this low in many other locales.
2. I don't have a number for the percentage of illegal immigrants in Prince William County, but I believe there are many, albeit a falling number.
3. I am not convinced by the argument that illegal immigrants will try "especially hard" not to get caught, because they are illegal immigrants and do not wish to be deported. This argument has been used to suggest that two percent is an underestimate.
4. When all is said and done, two percent is a fairly low number.