When Columbo interviews Jarvis at his front door, Jarvis is barefaced while facing the camera but is wearing glasses in shots from behind him.
When Columbo is examining the mouthwash bottle, in the long shot where Peter Falk is fully visible, the bottle is shaped like a cylinder. In the closeups where only hands holding the bottle are visible, the bottle is rectangular, like a brick. Also, in the long shots, the bottle's label is solid yellow; in the closeups, the label has a white border.
On the divorce papers Columbo finds in Linwood's file (and later sent to him by Justin), Vanessa Galper's name is incorrectly spelled as "Vanesssa".
When Columbo is checking out Linwood's bathroom the objects over the sink - shaving foam, mouthwash, hair grease and two fake flowers - change between the full shot and the zoomed view.
When Columbo speaks with the police officer at the police station about when Tony Galper disappeared, he holds a cup in his right hand, then transfers it to his left hand and places it on the officer's desk. In the next shot, the cup is back in his right hand.
When Columbo returns to Linwood's apartment to go through the file cabinet, he merely tears down the police tape and enters the unlocked door. The crime scene would have been guarded or locked to preserve evidence and keep the public out.
Peter Falk was 76 when this was filmed and assuming Colombo was the same age, he would have been way past the LAPD mandatory retirement age.
Although a gloved detective is dusting the keyboard in the 'suicide' victim's apartment, Columbo wanders in and indiscriminately touches items in the bathroom, picks up and thumbs through photos and other items laying around. He even touches the desk calendar which the killer handled. He does all of this with his bare hands potentially destroying fingerprint evidence. Only afterwards does the gloved detective discuss with Columbo that the killer may have been wearing gloves based on the keyboard prints.