Federal law requires that an illegal alien be deported. So for state and local law enforcement not to report that person they found to the feds for deportation, regardless of their crimes, would seem to me to be conspiracy to violate US immigration law. While I'm not to the point of requiring citizen to report known illegal aliens, it seems that it's incumbent upon law enforcement to do so. After all, don't they fingerprint them when they're arreted and send those fingerprints to the federal authorities?