DHS is not very forthcoming with immigration statistics and other basic data. For instance, USCIS even redacts the names of lawyers working on appeals cases, as I reported recently. This general lack of transparency, unfortunately, is contagious, and it extends to how other law enforcement agencies report (or don't report) on aliens and arrests.
It's not that the aliens are not arrested, though sometimes that's a problem. It's that the immigration status of the accused, or lack thereof, is not routinely captured in the reporting systems. Without that data it makes it harder than it needs be to deport some aliens and makes it more difficult to formulate a sensible immigration policy.
Needless to say, the White House is not about to solve this matter, but Rep. Mo Brooks (R-Ala.) has introduced a bill to correct the situation. It's H.R.3151 and it does two things: First, it allows arrest reports already sent to the FBI by state and local governments to include the best known immigration status of the arrestee. Second, it requires the federal government to publish illegal alien crime data in the FBI’s annual crime reports.
Brooks's office told me that they have 11 co-sponsors of the bill, all Republican House members, and the support of several national organizations, including NumbersUSA, FAIR, and the National Citizenship and Immigration Services Council. The bill, unlike so many others, has a straightforward name: The Arrest Statistics Reporting Act.