"I think you know, Admiral." Because if Khan was willing to attack others here, injured and lashing out over his sudden arrival, what must he be like when he's in full control? When he's just found out his family has been killed?

"I always thought it strange that after an attack - say, a bombing - all of your senior officers would gather in one concentrated area. Daystrom presents a rather tidy target."

All the heads of Starfleet, right there for him to cut down.