It is a dismal failure of Intelligence agencies any time there is a terrorist attack perpetrated by jihadis anywhere outside the Muslim world. Extremist Muslims are vocal, obvious, and boastful. If you can infiltrate organized crime families, infiltrating radical Islamist groups could be done by an intern. These people are not the sharpest tool in the shed. Identifying and investigating such groups takes no great skill. There is just no reason why they cannot be shut down.