The device that likely sped up the carnage in Las Vegas

How was the Las Vegas killer able to shoot so many rounds so quickly? Stephen Paddock, the 64-year-old retired accountant who went on a shooting rampage, had stockpiled in his hotel room at least 23 firearms, as well as two bump stocks, which are used to modify weapons and make them fully automatic. William Brangham explains how these modifications work and how they get around the law.