Some people think their notoriety is overrated but I believe the Gemini twins were pretty feared and clever enough to stay alive and out of jail for as long as they did without cooperating.

I'm not sure how close Casso was to them, except that he was their boss/underboss but if shit hit the fan, I wouldn't be surprised if they made a move for the thrones, even though they were pretty young.

Casso mostly was killing informants based on tips, but not always. He'd also killed people based on suspicion alone.. plus I'm not exactly sure how much I believe his story about the FBI agent who used to feed him info for like 4 grand (a week? I'm not sure) It seems like a bullshit excuse so he could twist his story to appear better in the book.