There's always bombs. Tokyo subway attacks, skinhead in England made a grenade with screws and nails as shrapnel, ordinary Iraqis making IEDs, all these in countries with gun bans.
As I said before, people will always kill each other, and with plenty of websites showing you the formula for anthrax, or the proper way to make a fertilizer bomb, I don't think a gun ban will stop mass murder.
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