I'm curious, what exactly was going to make it harder for Adam Lanza to steal one of his mother's legally acquired firearms?  You must be talking about a ban on the weapon, since there isn't any legitimate reason to stop his mother from purchasing a firearm.  Maybe you need to do some searching and find out how often "assault rifles" are used in murders.  Of course once you do that you'll just want to ban handguns as well.  Doubt it will bother you though, you seem like the typical gun grabber... blame the NRA, blame gun owners, blame gun manufacturers... blame everyone except the person that actually committed the crime.