Ticking Time Bombs

So now it seems that this Alabama professor who shot up a tenure meeting shot and killed her brother as a young adult, a death that was ruled accidental.  She seems to have also been a suspect in an attempted pipe bombing of a Boston colleague.

This sort of crime haunts me.  All the signs were there, and no power to stop it.  And moreover, the government shouldn't have the power to stop it (I mean, short of finding evidence and convicting her).  But then what do you say to the families of those who died?