This is something you can go over repeatedly without arriving at answers, but whenever there's more than one motive for the murder, I can't help wondering which one "predominates."

When it comes to "Greenhouse Jungle," I can never help thinking that just plain greed isn't enough of a motive for the murder part (no matter how much greed Jarvis DOES have), or being that touchy about how Tony is planning to spend his share. Maybe this is common knowledge, but I think he simply considers Tony too much of a weak link (between himself and Gloria, someone is always calling him weak), so that even if they carry off the fake kidnapping, that won't last. So I always wonder whether either of the other two motives (especially the second one) would actually get Tony killed. Again, maybe that occurs to everyone, but I never seem to hear it mentioned.

Another is "Murder By The Book." The insurance money is definitely Ken's biggest motive, but is the grudge against James important very by itself? I can't help thinking that Ken is too "superficial" to let an emotional reason like that do any of the deciding, but is it possible?

I don't know that I've ever thought of the 'weak link' motive, but it is obvious how much Uncle Jarvis despises his nephew's perceived lack of backbone. I think I would lean toward Jarvis killing Tony for money and distaste. He really dislikes Tony and his wife. While getting the $300,000 is great, there must be some sort of perverse satisfaction in ridding himself of his annoying nephew once and for all.

As for Ken Franklin, I have always thought he wanted to kill Jim out of anger and as a sort of revenge. Columbo noted Franklin "never really showing any true emotion for a man you worked with for 15 years". At the end, when Columbo shows him the story outline which Franklin used to kill Ferris, Franklin temporarily relishes the attention, as it touches his immense ego (oh, look, even Lt. Columbo recognizes the brilliance of my work). However, it also sets off his feverish jealousy, as he indignantly remarks, "I must have shared that with him five years ago. Who ever thought that IDIOT would write it down."

This is a good topic to explore.