I can now claim vindication on my hunch about "Double Exposure" being scripted for two hours and then at the last minute being hacked to 90 minutes. The new book "Shooting Columbo" is out on Kindle now and the author has had access to all of the shooting scripts. For "Double Exposure" he confirms there were scenes at the beginning and that indeed this is where Arlene Martel appeared as Tanya. One important thing is that she was *not* in cahoots with Kepple's murder plot. Instead, as part of his broader attempt to frame Mrs. Norris, Kepple tells Tanya that Mrs. Norris has found out about her and is threatening her, so that's why she left the country. (There was also an earlier confrontation scene between Kepple and Norris where Norris, much like Mrs. Kennicutt in "Death Lends A Hand" was telling Kepple he wasn't going to be blackmailed any longer).
And as we also suspected there was material cut in the middle of the episode involving Kepple's attempt to frame Mrs. Norris for Roger's murder as well. After Kepple shoots Roger, he phones Mrs. Norris pretending to be Roger to get her to come meet her and thus this is to put her near the scene of the crime when Roger's murder is discovered.
I would have liked to have seen Robert Culp do an impression of Chuck McCann. I don't think the old "pinch the nose to sound nasally" trick he used the first time with Mrs. Norris would do the job here.
To me what's amazing is that the previous episode "Candidate For Crime" was basically bloated to two hours because it ran just a little over what was needed for 90 minutes and IMO that episode should have been 90 minutes while "Double Exposure" should have been left alone (the book unfortunately doesn't explain why this one had to run 90 minutes).