Please, note my emphasis- appears, seems. Based on a layman's perusal of news headlines, I've reached this conclusion. The conclusion seems a reasonable one- a shooter is going to get farther if there's no one with equivalent firepower. But I'm not certain the conclusion matches the facts.
So, what are the facts? Anyone got some statistics? Do mass shootings tend to occur more often in gun free zones? What impact to "gun free zones" have on crime within that zone? I've got my opinion, but I'd like to see some actual peer-reviewed statistics. Google is leading me down the path of "guy with a website" opinions and towards John Lott's book, More Guns, Less Crime.