I liked the logic and the irony to the final clue, but it still is only circumstantial. It may demonstrate Ken's possible possession of the idea, but that doesn't necessarily mean Ken actually decided to use that idea to murder Jim.

But what are the chances that there would be a word-for-word description of Ken's murder plot in the office if Ken really didn't do it? I would say that it definitely would look suspicious, and along with all of Ken's other strange behavior and the mysterious death of Mrs. LaSanka, it's possible that a jury in the early '70s may have bought into it all. That was still a few years before the forensic evidence era when juries had to rely more on their common sense.