Border Patrol Does NOT check if illegal aliens have a criminal records outside US!

The criminal background check conducted by Border Patrol is compared with known criminal record databases in the United States ONLY and is part of the processing of the illegal immigrants by their agency. This is done through fingerprint comparison. During the screening process, Border Patrol also routinely questions illegal immigrants on gang affiliations in their country of origin. Information obtained during this process is used to determine whether they remain in detention or released pending a hearing date.
http://www.murrieta.org/faqs/categoryqna.asp?id=38#572