Buying, Selling and Using Assault Weapons in the US

The International Association of Police Chiefs reports that high-caliber automatic weapons are increasingly common on the streets of American cities. Local police departments are fighting back with military-style armament of their officers.  But there's dispute about whether the arms race started when the federal Assault Weapons Ban expired three years ago or long before that. Was the ban really all that effective?  Are there other reasons both cops and criminals are more heavily armed?  How come so many US assault weapons are turning up in Mexico?  We hear from journalists, industry and policy and gun-safety experts.