It is very sad but these events are not really rare.  black bears are more prone to predatory attacks on humans not just in Alaska but in Canada also etc.  They have a more predatory instinct, I have lived among brown bears a long time here in Alaska and never witnessed what I have seen in blacks.  They are distinctly different.  A brown will attack and maul out of defense.  A black will attack, kill and eat you just because it wants too.  Every bear cannot be predicted in behavior and you can't exactly catagorize them all the same either, they all have different personalities the same as humans.  Killing four just to get one was a little much but I guess considering the terrain they felt they had no choice but I can also imagine how stupid they felt each time they realized they had the wrong one.