I wonder how the book portrayed Waldo. I know that in the book Waldo meets Laura for the first time in a court and helps her. So I wonder how close the Waldo character in the book is to the one we see in the movie as played by Webb.
But I do get your point here. For a man to kill a women he loves because of rejection it usually takes a very strong sexual attraction and the associated rejection. That type of attraction isn't found in the film.
I read the book several years ago and Waldo was just as acid-tongued there. I think Clifton was remarkable here. AS a young child I saw this one on TV and assumed the motive was jealousy because Laura was going to marry someone else. So the physical side may be underplayed very cleverly, but the older man really cared for Laura. Nope, he did not go for Andrews. Sorry - not just the potshots he took at him, but we really get the picture as it unravels. What a frightening thing to have happened! (WHat a terrible way to exact revenge, but do not want to spoil it). Though he is portrayed as a severe critic and lonely bachelor he was internally very lonely. Laura had all the wonderful qualities he had ever wanted in a woman.
Yes, I read the other things years later about Clifton. Aside from that, he enacted the top superb performance of his life when he actually became - for a brief time - Waldo Lydecker, the former cynic.