From the IMDb:
"The Most Dangerous Match"
As killer chess-champ Emmett Clayton sneaks into Dudek's apartment for the second time (to mess with the medication), he sneaks past a room where you can clearly see two figures: an older man with mustache in a white shirt, and a woman sitting on his front left side. The apartment is supposed to be empty.
Just one quibble on that item. It was Tomlin Dudek's hotel suite, not his apartment.
But let's get down to the splainin for those two people in the suite, within the "reality" of the TV Universe. (Forget the mundane reason from the Real World: that they were two members of the production crew.)
There's a very good reason why Emmett Clayton didn't see them....
They are ghosts.
I've spent the last 36 years in the hotel business, and I've heard enough stories about the spooks haunting both hotels where I worked. And there was one murder/suicide in that first hotel while I was on duty.
And that's what I think we have here. My theory as to who they were in Life: She worked for that hotel, maybe as a housekeeper. He was her husband. They could have been separated; perhaps in the process of getting divorced.
And one day he showed up while she was at work, finding her in that suite. Distraught that she was leaving him, he pulled out a gun and shot her dead before shooting himself.
And now their souls are forever bound to that hotel suite.
Since this 'Columbo' episode aired, shows with supernatural themes have flourished; so many ghosts have appeared in their episodes. And in the show that made this genre so popular, 'The X-Files', they had two ghosts who haunted a house for decades, especially at Christmas.
So it may not be a precedent, but it does support the idea that ghostly couples exist in the main Toobworld.
That's my splainin and I'm sticking to it.
My thanks to Steve Skayman for reminding me of this goof. And October is a good month to finally write about it.