Reply #21: I read an interview with him from some years ago ...

[11cents]

...in which he said that his father had had Alzheimer's, so that he worried about that "a little" as he grew older.

Alzheimer's tends to run in families. I think what most likely happened was that he was in the early stages and several bouts with anaesthesia accelerated the process.

I'm very sad about this too. He had a remarkably broad career, ranging from avant-garde and independent films to big Hollywood movies and, of course, TV. Really a legend, whose acting attainments went way beyond "Columbo" (but I loved that show).