The answer to that question isn't simple and is usually peppered with political points or incorrect information. We may never be able to stop such a tragedy from happening. Yet there is something we could do that could, at least, help police investigate when someone like James Holmes starts to purchase large amounts of tactical gear, guns and ammo over a short period of time. The best part is we already have a working model.
Financial institutions, primarily banks, must report suspicious activity when they suspect something might be afoul. This is due to the Bank Secrecy Act of 1970 (BSA), which dictates that any deposit over $10,000 must be reported, but that amount has been drastically reduced and is now discretionary.
Since the Patriot Act was signed, financial institutions have been encouraged to report suspicious activity in the amounts as low as $1,000-$2,000 to the federal government to help fight terror. The idea goes that terror groups could deposit several chunks of money below the $10,000 threshold in multiple institutions that a terror cell has access to, thus bypassing the original set limits in the BSA. This system works well, and it has enabled law enforcement to uncover money-laundering schemes in many instances across the country.
So what does this have to do with the Batman Shooter? James Holmes had a large volume of deliveries in the months leading up to his attack. Holmes also purchased several guns and 6,000 rounds of ammo several months before his attack. What if just like the banks, tactical gear, guns, and ammo sellers were all linked to one database that could be used to alert local law enforcement of unusual or suspicious purchasing of a literal cache of weapons that could be used for a mass attack? Could Holmes purchases have been alerted to local law enforcement that could have then opened and investigation into whether or not Holmes was a threat? Could this tragedy or a future tragedy be avoided if such a system existed?
It is hard to answer those questions honestly. Even if such a system existed prior to this incident, Holmes may have slipped through the cracks. Maybe local law enforcement would have gotten an alert and ignored it. It is really hard to say. For the question whether or not a system could help to stop a future incident, I think the answer is an unequivocal yes. So why not do it?
For one, it would be costly. It would require all tactical gear, guns, and ammo sellers to be linked into one system. That means additional regulations and cost associated with selling that type of product. It also means that private transactions would no longer be private in some scenarios. Privacy rights activists would come out in full force against such an idea. Finally, it would not stop or ban additional guns or gear from being sold, but only alert local authorities if the purchase or string of purchases is suspicious. This won't satisfy many gun control activists whose goal is to get guns off the streets.
In my view, this is a perfect example of a good solution with no support because it doesn't please both sides of the aisle. The right will say it's an invasion of privacy, and that the government shouldn't add new regulations. The left will say it doesn't go far enough and doesn't stop guns from getting into people's hands. Instead of compromising and coming together, both sides will bury they heads and take their corners. Until we get a Congress that can work together, I don't see anything being done. It is quite sad we've gotten to this state, when Congress cannot get together and work out a deal on big issues. Maybe things will change in November.