Madison Allen has learned not to listen to true crime podcasts while riding the bus to her Uptown bartending job.

“I look around and I think everyone looks like a killer,” said Allen, of Minneapolis.

Allen is particularly fond of “The Last Podcast on the Left,” which she listens to “obsessively.” The podcast has more than 300 episodes featuring three hosts who chat about serial killers, cold cases and tales of Satanism, the occult and conspiracy theories.

“Their research is awesome; they dig up details from multiple sources and look at all sides of a crime,” Allen said. “It’s fascinating to try to get inside the psyche of people who could do things like what they talk about.”

Allen is part of a rapidly expanding audience eager to plug in their earbuds and download gripping audio stories about missing coeds, butchered lovers and human monsters who prey on the innocent and unsuspecting.

Murder, from the headline-grabbers to the obscure cases, has long been a television staple, with “48 Hours,” “Dateline” and an entire cable channel, Investigation Discovery, devoted to telling and retelling morbid stories of shootings, stabbings, beatings and contract hits. Recent bingeworthy documentaries on Netflix and HBO have further fired up fans of coldblooded tales.

Now podcasting has become the latest evolution in the genre for those who want to hear a gory story while they drive, fold laundry or walk their dog.

“The long history of the genre goes back to True Detective magazine,” said Laurie Ouellette, a professor of communication studies, cultural studies and comparative literature at the University of Minnesota. “Every version of a crime story uses the same markers — descriptive information, suspense, building in clues and cliffhangers, finding the story’s heroes and villains and then packaging it as entertainment.”

With just a few clicks, anybody with a smartphone can download an ever-increasing number of true crime podcasts that explore disturbing tales of loners, prowlers, peepers, creepers, stalkers, slashers, pedophiles, mass shooters and madmen who populate the whodunits.

These podcasts, however, are a sharp departure from the audio storytelling of traditional radio. Over-the-air broadcasters must adhere to FCC regulations and few risk using the public airwaves for content that is unapologetically grisly, graphic and gruesome. Even radio programs considered racy seldom venture beyond PG-13 ratings. But with no oversight or uniform standards, podcasts can venture into hard R territory. And listeners seem to love it.

“The shocking details and graphic accounts of this material lend authenticity to the form,” said Ouellette. “We’re living in this post-truth moment, when there’s great anxiety and debate about what’s true and what isn’t. These stories feel real and listeners want that now.”

The intimacy of listening

The intimacy of audio heightens the impact of true crime stories, said Ian Levitt, a former radio program director.

“Podcasting is radio unbound,” he said. “Listeners develop a relationship with the podcast host on topics they’re already interested in. It’s audio on demand, like Netflix in your vehicle.”

Levitt is so convinced of the ascendancy of podcasts that last year he founded Studio Americana in Golden Valley, a professional audio studio, complete with producers and directors, which can be rented out to people who want to make podcasts.

And he counts himself among the platform’s many fans. “With the podcasts I’m into, sometimes I wish my commute was longer.”

The exponential growth of true crime podcasts started with the viral success of “Serial” in 2014. Host Sarah Koenig hooked listeners as she sifted through clues of a cold-case murder, ultimately leading to a pending new trial for the man convicted of killing his ex-girlfriend when both were teenagers in Baltimore.

Part of the magic of “Serial” was its ability to take the audience along on a journey of discovery. In one memorable scene, Koenig and her producer are recording while they drive the route the accused killer would have taken, putting the listener in the car with them while they try to figure out if he could have gotten from one place to the next, as asserted in the prosecution’s timeline.

“That’s what’s called active tape; it’s an effective tool for telling a story as it is unfolding,” explained Alex Kapelman, podcast consultant and adjunct professor in the Audio Reportage program at NYU.

“I love that kind of narrative-rich story. It lets you enter a world you can’t get into in any other way. It’s happening inside your ears, stimulating your imagination,” he said.

A dangerous habit?

Of course, there is a wide range in quality of podcasts.

Some true crime podcasts are put together by producers skilled in interviewing and with the know-how to round up recordings from police radios, 911 calls and interrogation-room confessions, creating full sound immersion for listeners.

The crime chat format is simpler and far cheaper to produce, typically involving a few hosts who retell and react to a murder story they’ve cribbed from true crime books, documentaries, even Wikipedia.

The overall number of podcasts available for downloading from the iTunes library is nearing a half-million. Edison Research recently put the number of Americans who listen to podcasts at 73 million, more than double the number from five years ago. And while there are no statistics on true crime podcasts, murder programs are consistently among the most downloaded shows.

There are enough of them that listeners loyal to the genre could indulge in a steady diet.

But listeners should beware:

“I haven’t seen research on podcasts, but the research on true crime television has shown that the more of these programs a viewer watches, the more they believe crime is out of control and they’re in danger,” said the U of M’s Ouellette.

“These programs tell listeners everyone is a potential criminal and everyone is a potential victim. That shapes the way people think.”

Kevyn Burger is a Minneapolis-based freelance broadcaster and writer.