Why are personnel living in installation housing at Andrews AFB allowed to store weapons in their quarters?

I would be more concerned with the security failures that allowed the unauthorized intruder access to the installation and sensitive areas.

If Andrews AFB allows weapons to be kept in the homes.....better question though: How was the perp able to get onto base?

Except in a few situations overseas, all people living in the barracks must store weapons in the arms room. However, this usually doesn't apply to on-post housing.

You have to register your weapon with the police if you are keeping it on-post and can't carry unless transporting them from point A to point B (i.e., unloaded, out of reach, etc), but all (at least, that I know of and I haven't been able to find any otherwise) military installations do not require people living in on-base housing to keep them in an arms room (JBA doesn't).