"We can go out on Twitter and there are loads of people saying insane stuff, but how do you know which is the one person? It's always easy after the fact, to go: 'That was clear.' But clearly everyone spouting their mouth doesn't go and shoot up a synagogue," said David Chipman, a retired agent of the federal Bureau of Alcohol, Tobacco, Firearms and Explosives and now senior policy adviser for the Giffords Center.