Lone Gunmen Always a Law Enforcement Challenge

The lone gunman keeps law enforcement officers across the country awake at night.
He's hard to pick out of a crowd. He has no criminal record. Often, he hasn't told anyone about his plans. He's compiled a weapons cache legally. He doesn't show up on any law enforcement radar until after he's acted.

Source: ABC News
Read more: http://abcnews.go.com/US/wireStory/lone-gunmen-law-enforcement-challenge-16830696#.UAv-2ng0e5A