Well, we should all recognize that the US Border Patrol and the INS have
a list of KNOWN international criminals with their names and pictures
coded on the computers that scan everyone's id (citizen or not) that
comes in. If there is a match, the person is shunted aside for further
questioning.

No the system is not foolproof in that a terrorist with no prior history
can easily enter the USA from Europe, Canada, Mexico...... There is no
foolproof system to keep a terrorist out!!!

Known criminals CAN be dealt with by proper information sharing between
nations.