I think RS is by far the most likely Zodiac suspect. I hope to see more investigation into his background.
Not only does he match the sketch, and could have gained weight or lost weight during those years, depending on his mental condition at the time, but the letter commended police for finding his Riverside killing, seemingly an acknowledgement of something he did not plan to divulge, and a much more personal and brutal slaying, as one might expect with someone he probably worked with or had known.