Try reading a better article about the fight. The murderer cut everyone in line. The mailman called her a name for gay men I have been called thousands of times over fifty years. She spat on his face (note this is assault in NY so this is the instigation of the fight). The mailman strikes her several times while bystanders attenpt to break up the fight. The murderer then grabs a knife and stabs the mailman killing him.

Things to keep in mind-

The murderer has a history of violent knife crimes.

The murderer is a physically larger person than the mailman and height and reach are two of the three factors we track in boxing and other fighting sports so thete is less of a belief that their life would be in danger.

Finally and this is the most important part _There is absolutely no self defense claim permitted in court where an armed person kills an unarmed person especially with a knife. _