If I lived in these apartments, I would plan on moving ASAP.
Nothing like advertising your renters are are prey for thugs
Sounds like that was already pretty well known in the area.
Many leases contain such clauses, but there is an implicit exemption for self-defense cases (to explicitly forbid self-defense would be illegal; many contract clauses are routinely interpreted as including such exceptions as may be required by law). A clause forbidding firearm ownership might be a trickier thing to judge, legally, since there's seldom any way to prove in advance that a self-defense situation is going to arise. In this case, however, a situation did arise and the police seem to have ruled it a legitimate use of a firearm in self-defense.