That's funny. Because usually when someone turns down the boss position it's because they want to fly under the radar and dodge any heat but Casso was front and center with Amuso, virtually inseparable when Amuso was on top, and then later did things to undermine Amuso. Some say it was Casso that ratted out Amuso's location to the feds so he could take the #1 position. But by then I guess he had nothing to lose because he knew the Feds were closing in on him too.

Basically if his reasons for turning down the boss position were to lay low he didn't do a good job of it. He basically used the power he already had as carte blanch to settle scores and remove Amuso's rivals.

Isn't he also suspected in the murder of Patty Testa who was close to Vic?

I invoke my right under the 5th amendment of the United States constitution and decline to answer the question.