In her book This Family of Mine (and this is mere speculation on my part) she claims that instead of Gotti being a renegade and taking out Castellano on his own that it was approved by The Commission with the exception of Gigante. We all know Gigante was unhappy about this and used the fact that Gotti broke the rules by taking a boss out. However, Gigante used Casso, a puppet to use a car bomb which is also against the rules to try and take out Gotti. Why would he try and insulate himself by doing this and using Casso as a proxy if it was in his right to kill Gotti by trying to make it look like he didn't order it? The Genovese also did something similar with Caponigro.

Then there is the instance of Gotti and Gravano meeting with Scarfo claiming they "got the ok for the hit"...Yes, they could be lying of course but it was also known people were unhappy with Castellano.

Then there is the issue that Victoria Gotti is just trying to make her dad look better and might not be credible because her version might be bias. Her book for the most part is surprisngly well written because I did not have a high opinion on her before but I was thinking about why Gigante would take those measures if he knew he was doing the right thing.