 CBS NEWS NATIONAL SECURITY CONTRIBUTOR SAMANTHA VINEGRAD TELLS US IF CROOK WAS ACTING ALONE, IT MIGHT HAVE BEEN DIFFICULT TO GET A WARNING. LOAN ACTORS ARE NOTORIOUSLY HARD TO DETECT AND HARD TO PREVENT FROM ENGAGING IN VIOLENT ACTIVITY. THEY TYPICALLY DON'T TALK TO OTHER PEOPLE, SO IT IS HARDER TO DETECT AN INDIVIDUAL WHO ISN'T IN COMMUNICATION WITH OTHERS. THE FBI SAID TODAY THEY ARE NOW INVESTIGATING THE ATTACK AS A POTENTIAL ACT OF DOMESTIC TERRORISM.