[Something inside Donatello, some kindness bludgeoned into him by the family he surrounds himself with, keeps him from correcting Casey on that point. His Leo's orders didn't keep them alive. They all died. Whether that was because it was just beyond achievement or because Leo's orders weren't good enough, Donnie will never know.

But fine, sure, Casey wants to ask him that? Donnie's given it thought. He leans forward, jabs a finger down atop Casey's detention slip, pinning it to the table.]

I don't care that you thought it was the best choice, and I don't care that Leo was begging you to do it. I don't care how you felt, what you believe was inevitable, or what went through your head while you were debating should you, shouldn't you. I don't even care what you should have done.

You showed a willingness to sacrifice my brother. [Donnie leans back in his chair, looks away across the library.] I don't hate you for it. Just know that if circumstances align to make such a choice necessary for you again, no matter how dire they should be, I'll remove you from the equation before you can make it. [Casey just can't be trusted to make the right call by Donnie, which is (always and forever), family first. No exceptions, no matter what anyone else says, including Leo.]