[3Fingas]

I think this guy was just a nut case with anger management problems. He slipped through the cracks because, apparently, he was fairly smart and could explain away some of his misdeeds. He probably went on a rampage because someone offended him. Since he was a nutcase, he couldn’t let it go. The anger probably mounted and he formed a plan to get even in his own warped mind.

[USNBandit]

I don’t know how you slip through the cracks on a Secret clearance. A BCI should have popped up his arrests and he shouldn’t have been granted a clearance. Chances are somebody got behind and signed off the paper without running the check.

[digger48]

He slipped through the cracks because, apparently, he was fairly smart and could explain away some of his misdeeds.

It happens all the time if one fits the correct "profile"