The 9/11 terrorist all came here on some form of visa. The fact that we have not done a better job of checking on the status and whereabouts of the person who get issued any form of visa just shows you how serious .Gov is.
On 4/19/2013, friends of Boston Bomber Jr., Tazhayakov and Kadyrbayev, were arrested for student visa violations. They and a female were handcuffed and taken in for questioning by the FBI but were shortly released. A few hours later, the female left in an unknown consulate vehicle. Kadyrabyev’s car tag was, “Terrorista #1”. Tazhayakov had had his visa terminated in 12/12 by HS but he was let back into the country on 1/20/13 by US Customs after being gone during Christmas break. Who knows if they’re still roaming US streets or what.