The floppy disc that Wade takes from his office is different from the one he uses to plant the story on Budd's computer. The disc, when he first takes it, has about 5 stories written on the label with a blank line between each title. When he takes it out of his pocket at Budd's house, there are more titles written on the label with no blank lines between them.
The camera in Wade's office is on a motion detector. In the beginning of the movie, the camera does not turn on until Wade enters the room. Later, when he is editing the surveillance video, the camera records him walking up to the door and then opening it from the outside, even though the camera wouldn't have been recording at that time.
While Columbo is showing the used cigarettes to Wade Anders, the shape and size of the butts keep changing.
Wade prepares for the crime by burning down four cigarettes and putting the butts in a baggie. At Budd's house, he doctors the crime scene by putting these butts into Budd's ash tray. At this time, there are six butts in the baggie.
At the murder scene, when Columbo notices the computer, the screen shows about one paragraph of writing on it, maybe 5-6 lines. The shot then switches to a close-up, and the screen shows two paragraphs of writing. The shot changes back to a further away view, and only the one paragraph is there.
Twice, once by Anders and once by a police officer, the Print Screen button is pressed. Both times what is printed has the title ("Escape to Death") in a larger-sized font than the rest of the text. However, on the screen, the title is the same size as the rest of the text.
When Columbo hits Anders' car, he dents it at the edge of the front of his hood. Yet this is recessed compared to the bumper, which protrudes from the car. And since both cars have bumpers, it is they that will make contact with each other, not the hood of Ander's car (this is, after all, the purpose of bumpers). Columbo's car would have had to have something on his hood, which would have protruded, to make contact with the hood of Anders' car. As Columbo's car has nothing on it (on the hood) that protrudes, Columbo's car could not have possibly made this damage. Columbo, an experienced detective, would have known this, and would not have accepted Anders' accusation that he (Columbo) made the damage to his (Anders) car.
When Columbo asks for a copy of the story on the computer screen, an officer pushes "Print Screen" on the keyboard. The screen then shows "Printing File". The "Print Screen" key prints only what's on the screen, not the whole file.
While Columbo is putting his car in gear, grinding gears can be heard, yet his right hand is visible on the steering wheel.
Anders could have simply removed the poisoning cigarette from Clarke's hand, and leave. Instead, he starts planting his own cigarette butts into the ashtray, and even one into the victims hand. An experienced Crime Psychologist as Anders, would never plant items that could incriminate him self, to a clean crime scene.
Even as a non-smoker Wade would surely have known the smoke had to go through the filters.
When Wade sets up Budd's office post-crime, the first thing he tends to is the cigarettes, pouring ashes into Budd's ashtray and stirring them up with his gloved fingers. He subsequently touches the keyboard, printer paper, and Budd's arms, clad in a light-colored suit, among other things. When the crime scene is processed, nobody finds ashy remains on any of these things, as would be expected.
When Bud Clark talks to Wade at the beginning, it sounds if he says Polly does Houston instead of Holly.
The lady in the pet shop impatiently asks "Is Sebastian ready yet?" Sebastian is presumably a male dog, but the attendant responds "I'll go get her."