Columbo (season 6)

Egocentric actor Ward Fowler (William Shatner), who portrays Detective Lucerne on a weekly TV show, is being blackmailed by his producer and ex-paramour, Claire Daley (Lola Albright), over the fact that he was a deserter in the Korean War. Fowler decides to kill Claire. He drugs a friend staying at his house watching a baseball game, puts it on tape delay, then dons a ski mask and pretends to rob a delicatessen where Claire is shopping. After Fowler knocks the proprietor unconscious and takes Claire's money, he shoots her dead, then ditches the gun and mask. He begins stepping in and out of character to "assist" Columbo with the investigation.

Final clue/twist: After Columbo has shaken Fowler's alibi, he confronts him with the fact that although there are no fingerprints on the murder weapon, there are fingerprints on the live bullets inside the revolvers chamber, Fowler had to insert for the blanks.

Ruth Lytton (Joyce Van Patten) kills her older brother Edward (Tim O'Connor) after he decides to sell the family business, the Lytton Museum, to which Ruth has devoted her entire life as curator. She hires Milton Schaffer, an ex-con who worked at the museum, to stage a robbery at the museum. During the robbery she double-crosses Milton and shoots him dead. She then kills Edward when he comes to investigate the gunshot. Her plan is to make it look like the two men killed each other in the middle of an attempted robbery. Celeste Holm plays Ruth's older widowed sister, Mrs. Brandt, who faints whenever the word homicide is mentioned, and Jeannie Berlin plays Ruth's niece, Janie Brandt. When Ruth realizes Columbo has not fallen for the staged robbery, she tries, out of desperation, to frame Janie for stealing valuable items from the museum and killing Edward to cover it up.

Bertie Hastings (Sorrell Booke) discovers that his friend, Oliver Brandt (Theodore Bikel), a senior partner in an accounting firm, has been embezzling money to support the exceedingly expensive lifestyle of his beautiful wife, Vivian (Samantha Eggar). Hastings refuses to remain silent, notwithstanding his friendship with the volatile and egotistical Brandt, who then plots Hastings's murder at the Sigma Society, the headquarters of a Mensa-type club for geniuses, trying to make it look like a burglary gone bad.

Final clue/twist: Columbo uses Brandt's own Mensa-level intelligence and vanity to trap him. After Columbo presents his (ridiculous) solution of how the murder took place, a nearly apoplectic Brandt shows him how it was really done - basically confessing the murder.