Columbo also suspected Dale because of the high heels going down the back stairs,what burgler/murderer wears high heels to a house break in.That is why he set up the demonstration with the policewoman and the security guard said that was what he heard.He knew he had a helper and that he was setting up an alibi by asking the valet to look in his trunk for his cufflink and making sure for people to know that he was at the gallery at the time of the murder by asking the time.