Cass was rather forcibly biting his tongue to keep from saying anything that would keep this idiot of a man from donating more money, yet Dolohov was making it quite hard not to want to hex him to the other side of the room.
Even if he hadn't been talking about killing a friend of his (even if it was a Death Eater friend of his) just the talk of putting people out as if they were nothing more than animals got him annoyed.
'Well it may seem useless, we don't go around killing people, Mr Dolohov,' he said finally unable to keep quiet. Still he was glad for his father's training, since even now his voice showed none of his irritation. Rather he sounded pleasant, a bit amused, casual. 'Imprison them, by all means, but only when there is evidence against them as we prefer not to spend the resources we do have on potentially innocent people when we can spend them on the unquestionably guilty ones.'
He smiled. 'If you like to see us imprison more people I'd suggest donating more money.' Maybe he'd go away so he could talk to Percy alone.