To reduce the amount of bodies, and spares without partners. If I killed her and Kazuaki, my risk of death due to being unpaired went up-- and if the plan failed, I was still safe as long as we weren't caught.

[he looks a little offended, actually, because-]

She wouldn't have been hard to kill. There was just less personal risk involved... well, and then there's her position, but I didn't know that until after framing her.