According to one source, when Anastasia showed up at a Commission meeting and plopped down in Mangano's chair, he said Mangano was plotting against him. Could have been. Costello once called a Commission meeting to complain that Genovese and Lucchese were plotting against him and Anastasia. Gambino called a Commission meeting because Bonanno and Magliocco were plotting against him and Lucchese.
Anastasia was pretty bold about it too; Always shocked me that Profaci and Bonanno did nothing as retaliation. Mangano was a good friend of there's who went fishing with them occasionally.
I think Keeping quiet after the Anastasia hit was a sign of approval. I suspect they didn't mind seeing him go.
I also believe that Anastasia was whacked in such a brazen fashion, it was a sign of disrespect.... same disrespect he showed for his boss, Mangano and his brother.
