I would be surprised if the killer didn’t leave town. It’s the perfect opportunity to escape. People went home. Some might not come back. Disappearing wouldn’t be sus at all.
This whole thing seems… planned. It’s like the perp chose the perfect timing. Holidays are a messy period. People are moving around, going home, traveling, etc. There’s no order. It adds chaos to the investigation. This leads me to believe that the killer is not some opportunist nutcase who surrendered to his “urges“, but someone sound of mind who planned this whole thing very carefully. He chose the house, the girl (girls?), the timing. None of this was accidental.
IMO it’s a serial killer. Could be a student, a local, or a transient. Either way, I doubt he’s in town anymore.