Hi Xelor, I am afraid that your inquiry has a few built in fallacies that render an answer to your satisfaction nearly impossible to give. Firstly, you only want a "professional" to answer. A professional marksman? Those rare birds are generally only found in the serving military. I doubt there are many, if any amongst our posters on USMB. A professional psychiatrist? A psychiatrist would not give an off the cuff opinion on the sanity of a person under any circumstance without a one on one evaluation, not counting again the fact that there are probably none here. The only person that can speak to motivations of the shooter was the shooter himself, and he will shortly be pushing up the daisies. His cookie crumb trail speaks to his desire to kill. That all being said, I believe I can shed a bit of illumination on the thought process of the shooter through his selection of weapons. There are two main popular types of "assault rifles" available on the market commercially. 1) Kalashnikov types based on the AK family 2) Stoner types based on the M16 family (AR) Please keep in mind that other than visually, there are very few similarities between a commercial version of either of these weapons and those used on the battlefield. Both types of weapons were developed as a result of real world feedback regarding the use of individual firearms on the battlefields of WWII. The traditional military rifle, the bolt-action, was a reliable, robust weapon that could theoretically hit targets up to a 1000 meters away. One shot at a time, with a full sized, heavy cartridge. During the war it was discovered that soldiers were not engaging targets at ranges much beyond 300 meters or less. Further it was learned that well aimed single shots were not as effective as volume of fire. The full sized cartridge was in fact too powerful. Thus the Germans developed the first "assault rifle", the STG44, the grand-daddy of all modern military rifles. Gas operated, special small cartridge, stamped metal components. The requirements: 1) Portability 2) Volume of fire 3) Ammunition load-out 4) Economy of manufacture 5) Economy of maintenance 6) Accuracy Please note that these are not in any particular order, indeed, which requirement that was considered the "key" by each designer plays an important part in my conclusions. The Kalashnikov variants, in true Russian fashion, rely on economy of manufacture and maintenance followed by volume of fire as the main requirements. Accuracy, not so much. They were designed to be operated by illiterate grunts after being drug through the mud and dust for days without cleaning. They make up for lack of accuracy with a greater rate of fire and they fire an heavier round with more ballistic energy. They tend to cause through and through wounds. Russian doctrine: saturate an area with fire, close for the kill. Finally, they are inexpensive. The Stoner variants are a whole different animal, despite coming from the same requirements. The M16 series call for portability, ammunition load out and accuracy as the most important requirements. The US Army, while agreeing that realistic battlefield ranges were only 300 meters, they still wanted to be able to hit that target at that range. Thus the M16 series were built with tighter tolerances with lighter weight components to fire the smaller round designed for it. They tend to cause more grievous non through and through wounds. US doctrine: destroy the target at a distance. Finally, they are expensive. Now, both types are commercially available in civilian versions. The AK's are much cheaper than the AR's. One is just as plentiful as the other. The AR is much more portable and a lot more accurate than the AK. Therefore, presuming the shooter was not a total loon, if all he wanted to do was spray lead without hitting anyone or anything, he would have more likely chosen an AK over the AR. He wanted to hit and kill, thus requiring the more accurate weapon. Despite Hollywood's enamorment with "assault rifles" hitting and killing anything they are pointed at, hitting a man-sized moving target is no easy thing at any distance. The victims were lucky this man was apparently a poor shot, because his weapon was capable of delivering a body count. My conclusion: he wanted kills, a lot of them too.