I also wondered about holes/irregularities in the building and if there were any crawlspaces or things of that nature. I would think that if someone in town came across a bloody hatchet or bloody clothing after knowing that there had been a murder that they would contact the authorities. Also, real blood has a smell that imitation Halloween blood does not have, so even on Halloween night it might be noticeable.
Maybe it is just me, but honestly, I have a bit of a problem with the theory that the person who murdered young Mr. Weiss because they didn't like Jewish people. They are putting themselves at a lot of risk to sneak into a building full of people, commit murder and leave the building without getting caught. I would imagine if someone was looking to murder someone just because they were a particular type of person, they would target someone living in a much less crowded dwelling. I think there must have been something about Mr. Weiss specifically that made the murderer angry (whether it was something real or something imagined).
I agree; seems to me if the killer was anti-Semitic, he would've killed more than one student. This case just feels personal; someone out to get Chaim and Chaim alone.