It's Our Friend DNA!
Am I the only moron in the world who cannot operate packing tape without somehow getting hair, lint, and assorted other fun stuff caught up in it? I would never be able to be a serial mail bomber or anything. There'd be enough of my DNA all over the masking tape to pinpoint me within at least three years. (Because, if we're going by Wichita standards, it takes 31 years to catch a serial killer.)