It wasn't an AR-15 or an automatic weapon. It was a common shotgun that Aaron Alexis used to carry out the Washington Navy Yard massacre earlier this month. We've detailed the history of that gun, the Remington 870, today. It's a worthwhile read, especially if you want a better understanding of the tools being used to carry out these horrific crimes. Similarly, we also published a history of the AR-15 rifle in December, following the Sandy Hook massacre.