 The biggest unknown here motive, CBS News has learned that the shooter here was part of at least one gun club in recent years. The T-shirt he was wearing boasted of a popular firearm YouTube channel. CBS's Nicole Skanga. CBS News national security contributor Samantha Vinograd tells us if Crook was acting alone, it might have been difficult to get a warning. Alone actors are notoriously hard to detect and hard to prevent from