Cali shouldn't have gotten involved with his niece's situation. Look, I understand how close many people are with their nieces, but I'm sure she had several other uncles, uncles without the responsibilities involving hundreds of people and millions of dollars that Cali had, who could have dealt with this. And if she didn't, Cali could have sent someone else to deal with it, particularly someone far enough down the totem pole that it would never lead back to him.
I think of Tony Soprano telling Paulie, "When are you gonna get it? You're a part of something big"... It's a business. A CEO never does a security guard's job.
I understand, but we don't know the niece's story, and we may never know it. Comello seems like a nut , so it's not a stretch to think he may have been stalking a woman. A young woman living on Staten Island NY related to a high ranking mob guy might not feel comfortable going to a police station to file a restraining order, she would talk to the uncle. I am sure Cali never thought it would play out like it did. Most people (even mobsters) would not think of slapping someone like Cali, much less clipping him. He must have thought talking to the kid would be the end of it.
