What we know - 1. Killer is of medium size based on strike point of the anchor. 2. Killer is extraordinarily strong based on the use of the anchor as a weapon. 3. Killer did not rob the victim.
Unless magic is involved. You have to change some of your assumptions in Law & Order: Baldur's Gate. We don't know if the lute belongs to the elf, and though money wasn't the motive, we don't know if something else was taken.
