If you don't follow the firearms debates in America, you wouldn't know that California (where the shooting happened) already has some of the strictest gun laws in the nation. And yet, these people were able to stock thousands of rounds of ammunition and build numerous pipe bombs.
Also, contrary to what you may hear from some "experts" ... In America, the safest places (in terms of violent crime rates) are NOT where gun laws are strictest. In fact, it is the opposite. That is why law-abiding residents of Chicago and Washington DC went to court to loosen gun laws in those areas - so they could more easily get firearms to defend themselves against the criminals. Because criminals don't obey the gun laws, anyway.