Paula Zahn, center, host of “On the Case With Paula Zahn” on Investigation Discovery, with an executive producer, Scott Weinberger, and the producer Emily Smolar.

Nobody who watches television would ever guess.

For programmers crime pays like no other genre; they are offering more homicides than ever — real murders, not those conjured by Hollywood scriptwriters. The documentary accounts of husbands slaying wives, strangers killing for sex or money, and people on drugs committing murder for more drugs have become a staple of weekly network television through series like “48 Hours Mysteries” on CBS on Saturday nights and “Dateline” on NBC on Friday nights. (The program’s Sunday edition doesn’t regularly cover true crime.) The genre has proved so popular that an entire channel, Investigation Discovery, dedicated to illuminating every gory detail, is now the fastest-growing in cable. ID, as it is known, grew 69 percent in total viewers over the past year.

ID draws its best ratings for “On the Case With Paula Zahn,” the channel’s first show to attract more than one million viewers. That weekly, step-by-step examination of elaborate murders is told in the suspense-building style familiar to fans of “48 Hours Mysteries” and “Dateline.” As it happens, both those shows (in the form of repeats) have spots on ID’s schedule. And all three series are still going strong in first run; together they allow fans to feast on over 100 new episodes of real-life bloodshed and mayhem a year.

But that number doesn’t even take into account other offerings, like “Unusual Suspects” and “Deadly Women,” that seem to prove, as ID put it this month in promoting its “Shark Week”-like programming bloc, “Shock Week,” that the real predators we should fear are one another.

While the broadcast-network series are not hits in the traditional sense, they fill time slots with more-than-respectable audiences for lightly viewed nights, with each averaging 6 million to 6.5 million viewers, more than those for “Fringe” on Fox and even “30 Rock” on NBC.

Both “Dateline” and “48 Hour Mysteries” are serious productions from the networks’ news divisions, with staffs dedicated to combing crime blogs, newspapers and legal records for cases juicy enough to be told in multiple acts.

And therein lies the appeal. As David Corvo, the NBC News executive in charge of “Dateline,” put it, “It’s got good guys, bad guys, conflict over something that matters, suspense and then resolution — the classic elements of drama and great storytelling.”

People “find the characters fascinating,” said Ms. Zahn, the host and an executive producer of “On the Case.” “They wonder why a pillar of the community could be driven to kill.”

Often said pillar is driven to bludgeon or shoot or stab his wife. “We have a slogan around here,” Mr. Corvo said, crediting a correspondent, Dennis Murphy. “It’s not about the murder, it’s about the marriage.”

“Dateline,” starting its 20th season in September, has carved a niche that Mr. Corvo confessed focuses on the emotional impact on victims and relatives. “It’s more about the jealousies, the disappointments, the alienation of people,” he said.

The “Dateline” style includes touches like cliffhangers before commercials and recaps after, often delivered in ominous narration. That’s certainly the signature of the “Dateline” correspondent Keith Morrison, the subject of a recurring “Saturday Night Live” sketch with Bill Hader, who portentously narrates while taking ghoulish delight in every frightening memory of his interviewees: “Oh no!” “Oh my!”

Mr. Hader didn’t have to do any research for the sketch; he’s a regular viewer of the true crime shows. “They totally suck you in,” he said. “They are way more bizarre than a ‘Law & Order’ episode. This stuff really happened.”

Mr. Morrison, he said, “has this folksy way of describing horrible stuff — like Garrison Keillor or Mr. Rogers describing the worst stuff imaginable.”

The “Dateline” staff can apparently take a joke. “We love Keith on ‘SNL,’ ” Mr. Corvo said. “It’s the best kind of compliment.”

Like most exaggerations, of course, it works only because it strikes close to the truth. “You have to remember,” Mr. Corvo said, ”these stories have taken the place of the movie of the week.” He added, “We see our show as a little nonfiction novel.”

If “Dateline” aims for your heartstrings, “48 Hours Mysteries” is out to elicit outrage at injustice. Susan Zirinsky, the show’s much-awarded executive producer, said that “what really resonates for us, what really floats the boat for the staff, is when you can make a difference.” That accounts for the emphasis on issue-oriented reports. “Our mission is to trace the tale of justice and see: where did it run amok?”

Several of the show’s reports have helped free the falsely accused. Ms. Zirinsky cited the case of Marty Tankleff from Long Island, who spent 17 years in prison for the murder of his parents. The show will do new reports as evidence arises, Ms. Zirinsky said. One frequent subject has been Amanda Knox, the American college student convicted of murder in Italy.

As early as 2008 “48 Hours” broadcast a report that concluded, as Ms. Zirinsky put it, “there is no way this girl could have done this.” (Ms. Knox won a new trial.)

Scott Weinberger, another executive producer for “On the Case With Paula Zahn” said the audience on ID tends to be hooked on forensics, and likes to “go along with the investigation.” That is, “We drop little bread crumbs through the story so you think it’s going one way and then all of a sudden — wow.”

The shows do bump into one another at times. Mr. Corvo said, “We might end up chasing the same story as ‘48 Hours’ 10 times a year.”

But that is not evidence that the quantity of compelling murders is dwindling. Still, Mr. Corvo added, “We’re involved in more cold cases now.”

None of the producers are worried about the supply of cases. “Unfortunately there is no limit on wrongdoing,” Ms. Sperrazza, ID’s executive producer, said. Ms. Zirinsky agreed, though she added that “48 Hours Mysteries” has in recent years turned to Canada, Panama and Italy for cases.

“If we get to a point where there’s not enough crime in America to support these shows,” Mr. Corvo said, “we all ought to be having Champagne, really.” But he was hardly ready to chill any bottles. “Human nature would have to change,” he said.