CLAUDIA SUTTON & VIVECA SCOTT
Claudia Sutton and Viveca Scott are identical cousins. (If they're both still alive, they're now close to 80 years old.) Claudia worked as a partner with Charles Lee Horne in running a top modeling agency, while Viveca had her own cosmetics firm as well as a "health farm". After Horne's murder, Claudia took over the agency as her own.
I would imagine that both Viveca and Claudia threw work towards each other. In fact, I think it's pozz'ble, just pozz'ble, as Mush Rat likes to say, that Claudia was a silent partner in that health farm. She believed in a strict regimen of diet and exercise, but secretly she cheated - with her concoction of carrot juice, psyllium, wheat germ, saurkraut, and dehydrated seaweed, Claudia would add a dollop of vodka to give it that extra kick.
Besides looking nearly identical* and being leaders in their similar fields of endeavor, Claudia and Viveca had something else in common: both of them were suspected of murder.
The only difference is, the "Lovely But Lethal" Viveca Scott was guilty. She committed two murders - that of a chemist who worked for her but who was stealing trade secrets from BeautyMark, and of a rival's assistant who tried to blackmail her. However, Lt. Columbo only arrested her for the murder of the chemist, for which he had her dead to rights. (She had been exposed to the poison ivy at the chemist's home.) I don't think he'd be able to prove conclusively that she killed the assistant without her admission of guilt (in order to broker a plea deal).
Claudia Sutton had everything to gain from the death of senior partner Charles Lee Horne, but in the end it turned out to be a low-life masseur who was responsible for killing the multi-millionaire. He also murdered his own "ex-wife" with the hope to pin it on Detective Tim Tillson.
After Captain Amos Burke solved the mystery of "Who Killed The Horne Of Plenty", he was free of ethical issues in dating Claudia Sutton. They were together probably only a few weeks before Burke moved on to his next conquest. Meanwhile, Claudia's cousin Viveca Scott would have been tried and convicted for manslaughter, probably only serving twenty years for the crime. (However, my compadres at The Ultimate Lt. Columbo Site believe she was found not guilty due to insufficient evidence.)
The actress who portrayed them both, Vera Miles, is still alive and so there's no reason not to think that both Claudia and Viveca are still alive as well. But who knows? Maybe the rigors of prison life took their toll on Viveca Scott......
'Columbo' - "Lovely But Lethal"
'Burke's Law' - "Who Killed The Horne Of Plenty?"
*Viveca had red hair and Claudia was blonde. Viveca's beauty mark was a fake.