I figure it’s mostly the electronics angle. Your phone, if you have it with you it’s really obvious if you travel to the area crimes happen. Heck, even not using your phone or other connected electronics can indicate something. Your car seen on surveillance cameras which are everywhere, from private home’s doorbells to commercial cameras to municipal roadway cameras. Your internet search history of maybe the victim or the location. Automatic toll payments. You’d have to live an almost completely disconnected life and take serious measures to avoid detection, and even then it’s not a sure thing.