Thoughts While Reading:
Okay, I like the concept of this being a letter, but some of the stuff at the beginning took me out of it a bit, because I feel like he is addressing the actual reader, someone that doesn't know him or even who he is intending this to be addressed to. If they all have the same mission, why would they think he's a serial killer?
You call Alice 'confused' twice.
"She started to flea..." Wrong flee.
I would take the quotes off killing. We already know it is what the accusers think, not him.
"Thinking quickly I looked at the picture again and then made up a story about not remembering her. “I'm very bad with faces.'"
I already got that he is lying here, so I wouldn't use it in the tag.
"ps. please burn this after reading as we do not want the enemy to know of us."
It's a nice touch, but it makes me wonder how he proposes to get this letter sent...
Overall impression:
This guy creeps me out so for once I am very glad this isn't going to be a novel. For a short piece, it works well and seems pretty clean. Great Job!