I was wondering how some were arresting illegal aliens (i.e., a sheriff's office) even when ordinances exist (whether voluntary or forced upon them via courts) prohibiting even asking immigration status unless it was a felon, etc., in effect, barring local law enforcement from immigration enforcement under the premise this is Federal Jurisdiction.
I believe section 287(g) provides some answers to that question.
For your local law enforcement :
Immigration Cross-Designation (Title 8) - 287g Program
http://www.ice.gov/exec/s287g/sectio...et_request.asp