The true-crime wave that has swept through culture didn’t start with podcasts. Long before popping in earbuds to stream “My Favorite Murder” or “Morbid,” Americans gathered on the couch to watch network staples like “Dateline,” “20/20” and “48 Hours,” which could turn shocking crimes into one tidy hour of television.

Dallas journalist Claire St. Amant knows all about true-crime TV, whose secrets she spills in her compulsively readable memoir “Killer Story: The Truth Behind True Crime Television.” As a former field producer for “48 Hours” — 48, as insiders call it — St. Amant logged time with serial killers, femmes fatales and cold-blooded husbands. “You have real talent for making friends with murderers,” a colleague tells her at one point.

In person, St. Amant is petite and younger-looking than her 39 years.

“I get mistaken for the intern a lot,” she says with a laugh. The advantage of being small and Texas polite is that people will underestimate you. St. Amant is cold-blooded when it comes to tracking down a lead, though.

“48 Hours” was in constant competition with “Dateline” and “20/20” to get the scoop, and the book lets us watch as St. Amant schemes her way past security and tries to sweet-talk attorneys into an exclusive.

“No one expects the little girl to get the big story,” she says, smiling, in a recent interview. “I just want to prove people wrong.”

St. Amant grew up in Katy, Texas, land of football games and outlet malls. In elementary school, she started a paper called Kids’ News, which she peddled around the neighborhood, enjoying the feeling of being the one with the information. At Baylor University, she studied English and journalism, graduating in 2008. She joined the Peace Corps and taught English in Ukraine, but when she returned a year later, the media landscape was dire.

One lesson of “Killer Story” is how much hustle is required for a job in 21st-century journalism, but St. Amant is dogged. She turned an assignment with People Newspapers, a chain of suburban Dallas weeklies, into a splashy exclusive for D Magazine, “The ESD Sex Scandal.” She landed a gig in 2012 at Culture Map, a lifestyle site with hubs in major Texas cities, and wrote a barn burner called “The making of the Keller black widow: Did Michele Williams get away with murder?” about a woman accused of shooting her husband and making it look like a home invasion in Texas. Not your typical fare for a website known for “fun things to do this weekend.”

The Williams story caught the attention of “48 Hours,” and a New York producer flew to Dallas to take St. Amant to dinner. He offered her a consultant position for a segment on “the black widow,” and she eventually became a field producer for the series. At first, she leaned hard into fake-it-till-you-make-it, but she evolved into a seasoned reporter with a knack for bending the rules without breaking them. She was also a young mother during these years, pumping breast milk in an empty courthouse room and taking a jailhouse call while bathing her son.

Part of the thrill of “Killer Story” is watching this underdog from Dallas scrap her way into a full-time gig at “48 Hours” and beyond, with segments that aired on the CBS morning show and “60 Minutes.” The other thrill is learning what a viper’s nest true-crime television can be. The pressure to win, the in- fighting, the calloused nature of some producers. St. Amant doesn’t pull punches in her depiction.

“As journalists, we speak truth to power,” she tells me, “and sometimes that power is a major news organization.”

Although the memoir is about the thrill of true crime — puzzling out a mystery, the study of human behavior — it’s also about its dangers. Ruminating daily on the evils of the world can do a number on the brain.

“Parkland broke me,” she says. “That was the beginning of the end.” Covering the Florida school shooting was one of her worst TV experiences, not merely because the story was so tragic, but because she felt she didn’t belong there. She was a voyeur, an intruder. “All the things I didn’t want to be as a journalist.”

Four more years passed before she left “48 Hours.” She had a mortgage, a child and a coveted gig in a tough profession. But how many spousal murders can one woman cover? At one exhausted point, she blurted to her husband: “I feel like we’re trafficking in tragedy, and there’s no redeemable quality to the story.”

She has softened her stance since then. She feels good about a lot of her work, including her episode on the attempted assassination of Julie Kocurek, an Austin, Texas, judge who used her near-death experience to push for legal changes.

“I recognize a lot of journalism can sensationalize these crimes, but that’s never been my goal,” St. Amant says. “I want to examine these complicated, messy stories and find the humanity.”

A few years ago, she started — what else? — a podcast. “Final Days on Earth with Claire St. Amant” lets her focus on stories she’s passionate about, like the first season’s subject, Dammion Heard, a former wrestling champion at Fossil Ridge High School in Keller whose mysterious death was ruled a suicide. She’s also developing a true- crime television series with a cable network, and she hosts a second podcast, “Justice Pending,” about cold cases and missing persons, with a woman she calls her “true-crime bestie.”

The waves of true-crime drama keep crashing to the shore. “Serial” becomes “Dirty John,” the Murdaugh murders become Ruby Franke’s child abuse. St. Amant understands why women, in particular, gravitate toward it.

“I think it’s a safe way to take in all the awful things that could happen to us and kind of desensitize ourselves,” she says, although she does offer a word of caution. “The hardest part about murder is that in the end, it never makes sense. There’s this misconception that we can ‘understand’ violent crime and put the pieces together in a logical sequence. But in my experience, it’s always chaos.”

That doesn’t keep her from listening, or growing obsessed with this or that case. There’s one place she won’t be getting her true crime, however.

When I ask if she ever watches “48 Hours,” she smiles and says, “I just can’t.”