Here is one where a guy murdered a young girl for breaking their engagement, in Ohio, and there was stabbing, but no river involved. https://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=11500870 Seems to be a case of life imitating art as this took place in 1869 and some versions seem much earlier, and it was the brother who witnessed the attack from a distance, not the murderer, who was named Willy.

Link fixed. -Joe Offer-