Most of it's simple enough to do, if not to think up. You write the letter. We all saw how he took Damien's death, we know he's an easy target. Slip it under his door. I don't know about everyone, but I don't go out the day before one of the Professor's deadlines, so I imagine there might be fewer eyes around that night for you to attach the brackets and rope for your trap. You set the strange lighting to make it easier to mistake who you are in the dark.

What really points to you, Anna, besides your hair, is... I saw you making all those clothes. Easy enough to hide a shirt in that pile, wouldn't it have been?