There are tons of reasons to be a fan of Cold Case. Kathryn Morris smolders as the complicated Dr. Lilly Rush. Her story unfolds against a staggering background of period pieces that stylishly transport you in time, whether it’s to the 1920s or the 1980s. All around her, the other characters are introduced as doubles, so viewers get to see both the version of themselves that Rush is interviewing now and the version of themselves she’s investigating in the past. Plus, the soundtrack always rocks.

It’s a show that burned slowly and drew rave reviews by its third season. That’s when New York Magazine gushed, “Cold Case is not only operatic, with a different bloody libretto and a different leitmotif each week, but has ambitions on the grander scale of Gesamtkunstwerk, of total Wagnerian theater—including a jukebox time machine.” That’s a fancy way of saying: This show rules.

But for today’s true crime-obsessed TV fans, there’s even more appeal to Cold Case in its episodes that point to specific cold cases in the actual real world. In season four, there was a particularly fascinating case that Cold Case brought to life, the true story of two serial killers who met when one half of the deadly duo posted a “lonely hearts” ad.

“Lonely Hearts” comes mid-way through Cold Case’s fourth season. It’s about a woman named Martha whose murder case is reopened when a suicide victim is found with a VHS tape of her playing in the background. The show dates this crime in 1989, and the hair is as big as the pounding heart the episode delivers.

It’s based on the American serial killers Martha Jule Beck and Raymond Martinez Fernandez. They were a couple known as “The Lonely Heart Killers,” and they are suspected to have killed at least 20 women from 1947 to 1949 by luring them with singles ads. There have been a few movies based on their bizarre back story, most recently in 2006’s Lonely Hearts, with Salma Hayek and Jared Leto filling the roles of the serial killers and detectives in John Travolta and James Gandolfini. Later that same year, TV viewers would meet the disturbing couple again through Cold Case’s lens.

The real Martha reportedly ran away from home as a teen, a period in her life when she hung out briefly with the writer Truman Capote, then only 10 years old. She eventually ended up back at home, as caretaker of her elderly mom, and that’s when a well-meaning friend placed the ad in the newspaper that led her to become a killer. Raymond responded to her ad, and the two began dating despite the fact that Martha soon learned he was a criminal. After that, Martha was so smitten, she even posed for a time as Raymond’s sister to cover up his crimes.

Their story is darker than even the fictions that are spun from it, and the pair was eventually convicted on just one murder count. The police connected them to 19 more, but they never confessed to those. Instead, they professed their love as their official last words, Raymond: “I wanna shout it out; I love Martha! What do the public know about love?” Martha: “My story is a love story. But only those tortured by love can know what I mean. I am not unfeeling, stupid or moronic. I am a woman who had a great love and always will have it. Imprisonment in the Death House has only strengthened my feeling for Raymond."