Mr Beck found time to obtain a gun. Seems he didn't concern himself with the responsibility to learn fire discipline, in particular to withhold fire when innocents are in that line of fire. This all should have occurred prior to this incident.
True enough that we should all be well practicised and think all these things through in theory as well as we can. How well we have taught our mind to think determines how well we will do when pressed.
However, much you would have condemned this man, a grand jury that heard all the facts did not find ~him~ to be the criminal in this case.