Just speculating but, is it possible one of those sticks (reeds) could have been used to strangle NC? It certainly would leave a mark on her as indicated. I would think it could even break the hyoid bone. Just for clarification, he could have done this from behind.
Who's to say they didn't have an argument and NC (if she did leave her phone on the key table) went to get her phone, who's to say BC didn't follow her, his anger building, and he grabbed one of the reeds and bam! - he strangled her!
Maybe way out in right field but just an idea...