After Jennifer Tupuola was attacked by her ex, Prosecutor Peter Carlisle stated that use of deadly force is justified when saving your own life or that of another. With that said, yes, deadly force is justified, but it still may not exempt you from a lawsuit from the attacker or his or her family, not to mention the time, money and effort proving your actions were justified, and that a life was in fact in jeopardy.
Regardless of liability, the fact still remains that NO action took place by any of the witnesses. One can argue the level of involvement when a preventive measure is taken, but none can argue the fact that a simple call to 911 would have given the victim a fighting chance. As everyone noted, a sad and nerve grinding situation indeed