Just when you thought we had put this one to bed...
How was the purchase of the weapon by a collector who sold it to a criminal the fault of the gun manufacturer? From this story, we don't even know if the collector had knowledge the man he sold the gun to was a criminal. The gun manufacturer sells to the cops, the cops sell to a gunshop, the gun shop sells to a collector, the collector sells to a criminal (did he know this man was a criminal?). That seems to be stretching the limits of liability, doesn't it?