Board Thread:Questions and Answers/@comment-35036766-20180318153913/@comment-1327106-20180319040946

I suspect that the reason he asked is that the enemy would not risk raising the possibility of a mole within the military ranks, so someone who did not know better or was the mole would not suggest that as a possibility. Since most people were writing off the incident as someone just hating Titans, that would be the preferable story for the mole to support.

But someone who was aware that the deaths were because of a mole, and was willing to bring up the possibility, could be useful in trying to capture said mole. Erwin could safely eliminate that kind of person as a suspect and enlist their help.