My theory has always been that he DID see the flower under the piano but left it there as bait. When the Maestro picked it up he implicated himself, which explains Columbos' subsequent focus on him as the prime suspect. Cass, do you agree??

wow! steve that is very interesting. i had not thought of that before. i went back and looked at the scene again, keeping close attention to where columbo is situated during the scene. he checks the birdcage and sees that chopin is dead, and he is standing right by the piano and bench...there is no way he could have missed seeing the flower.
and then when alex benedict arrives and spots the flower, columbo is all the way across the room with his back turned. but then columbo turns around, as alex is pinning the flower on and he asks, "find something?"
columbo couldn't have seen him pick it up because he wasn't facing alex at that point, so there is a strong possibility that he knew the flower was there all along and trapped alex into picking it up.

terrific conception, steve! i like that idea a lot!