Found a link on this. Looks like Casso was the underboss and Angelo got shelved for this incident. I guess Gotti becoming boss went straight to Angelo's head that he thought he could whack an underboss of another family and get away with it. Insane.

Also, seems like Marino didnt know his nephew was involved, but later washed his hands of him once he learned of the failed hit.

Glad to have the history buffs here on the boards to correct me when I'm wrong!