I thought that it was possible that the culprit screamed instead of the victim, and took advantage of the panic it caused to run over to them and kill them, under the guise of seeing what happened. Who got to the body first wasn't made clear, I think.
I wrote down the train of thought that led to me solving the murders here: https://docs.google.com/document/d/15MobEUaJRZuDApsJfi936hlrjNZdPIxFLAlCjtVFDa8/...