The guns that lunatic used in the Aurora Massacre are not at all uncommon and can be purchased almost anywhere. The only weapon that’s somewhat controversial is the AR-15, and that’s because it was classified as an assault rifle for the purposes of the Public Safety and Recreational Firearms Use Protection Act. In other words, its sale would have been restricted or banned during the ten years (1995-2004) that the Federal Assault Weapons Ban was in place. That law restricted the manufacture and sale of semi-automatic weapons that had certain other characteristics. The AR-15 was covered by the law. However, it’s possible that the AR-15 used in this case was configured to be fully automatic, which would make it illegal under current law. Yet, I think this unlikely because they’ve tracked the purchase and it would not have been sold over the counter as a fully automatic weapon. Either way, the gun is extremely lethal.

It was made more lethal by the addition of a 100-round drum (“large capacity ammunition feeding device”), which was also banned under the Federal Assault Weapons Ban. In addition to his weapons and the drum, he was able to purchase 6,000 rounds of ammunition off the internet without, as far as we know, arousing any suspicion. His armor was also purchased on the internet, and it included neck and groin protectors in addition to a vest and helmet.

Going beyond his guns, ammo, and armor, he also was able to obtain tear gas and possibly smoke grenades. And these things are just what he brought with him to the movie theater. He also obtained oodles of other suspicious items that he used to rig his apartment as a giant bomb. We’ll know more about this shortly, now that the police have disarmed his apartment and gained entry. But we know that he had accelerants, triggers, probably timers, possibly land mines, and other bomb-making equipment.

In theory, all these purchases created a profile that would be possible to detect in advance, in much the same way that the government tracks purchases of large amounts of fertilizer that can be used to make bombs like the one used in the Oklahoma City bombing.

I want to be clear about a couple of things. I do prefer that most gun laws be set at the local level, meaning that cities may enact more restrictive laws than states as a whole, and that states may differ in the degree to which they regulate guns based on the political preferences of their subjects. I also am extremely wary of government snooping on our credit card purchases and internet activities. Wherever possible, I prefer the lightest possible federal government touch over our lives.

And I don’t think that the Federal Assault Weapons Ban was particularly effective, although I supported it because it was the right thing to do. My position isn’t really much different from Mitt Romney (version 2004) who signed a permanent Assault Weapons Ban in Massachusetts when he was the governor there.

“I believe the people should have the right to bear arms, but I don’t believe that we have to have assault weapons as part of our personal arsenal,” he said on Fox News in 2004.

In essence, even if an assault weapons ban isn’t particularly effective, I see no reason to make it easy and legal for people to own semi-automatic rifles and large magazines of ammunition. If you want to know why, look at what the people in that movie theater experienced, or revisit the 1997 shootout in North Hollywood.

But we shouldn’t focus exclusively on the weapon and ammunition. We should look at the whole picture. The best way to stop this guy wasn’t by making his task a little more difficult. The best way to stop him was to detect his abnormal activities in advance. We have the National Security Agency (NSA) scouring through records to detect the next airplane bomber from Nigeria or the next Timothy McVeigh. Why didn’t they notice that some guy in an apartment complex in Aurora, Colorado had purchased four separate guns, 6,000 rounds of ammunition, full body armor, explosive chemicals and components, and so on?

We all want privacy, but we understand, I think, that someone should not be able to acquire the components to make “twenty-five 55-gallon barrels filled with a volatile mixture of ammonium nitrate and fuel oil” without arousing suspicion, which is what the Oklahoma City bombers were able to do. Likewise, the Aurora nut job’s activities should have set off alarm bells.

This, of course, involves a debate about how much freedom and privacy you are willing to give up to buy a little security. Your chances of being killed at the movies are still incredibly low. And any system that can detect suspicious activities based on credit card transactions, point-of-sale gun records, and internet activities can be abused. But we’ve already surrendered most of this privacy anyway.

At least in the foreseeable future, no one is going to convince Congress to reenact the Federal Assault Weapons Ban, and it wouldn’t preclude tragedies like what we just saw in Colorado even if they did. But we might convince Congress that certain gun and ammo and body armor-related purchases must be reported so that it is easier to put the pieces together when someone is amassing an arsenal. We consider it suspicious and worthy of investigation any time someone makes a bank deposit of $10,000 or more. But we don’t consider it suspicious and worthy of investigation when someone buys four guns, including a semi-automatic rifle, 6,000 rounds of ammo, full-body armor, and bomb-making materials?

I don’t think that makes sense. People may have the right to bear arms, but they don’t have the right to create a personal armory without being investigated.