At least five Dallas police officers were killed and seven wounded July 7, after a peaceful protest over recent police shootings. Here's what we know so far. (Deirdra O'Regan/The Washington Post)

Wrong. Again.

Like so many times before, the initial news reports out of Dallas on Thursday night and into Friday were inaccurate. There were two shooters, the news people said, and then there were four. The gunmen had “triangulated” police officers guarding a protest march, and had targeted them from an elevated position.

Except “they” hadn’t done any such thing.

By midday Friday, new facts began to displace the old “facts.” Instead of two or four gunmen, police identified just one, Micah Xavier Johnson, 25, who (reportedly) died when police detonated a bomb sent in to his hiding place via a robot.

Contemporary media organizations didn’t invent misreporting (“Dewey Defeats Truman,” the Chicago Daily Tribune once infamously said), but misreporting seems to be a feature of almost every major breaking news event these days, from accidents to natural disasters to the man-made kind.

The victims of the Dallas protest shooting

Thanks to the speed and ubi­quity of digital media, readers, viewers and listeners know more than ever about any unfolding incident or disaster. But they also know less, thanks to the unfiltered, uncorroborated and just plain inaccurate factoids that poison the news ecosystem like a toxic chemical. It’s not just inaccurate reporting alone; TV news panels and people on social media compound questionable facts by repeating them and speculating about them.

“We keep relearning this lesson over and over,” says W. Joseph Campbell, a communications professor at American University and the author of “Getting It Wrong,” a book about epic journalism mistakes. “With any tragedy, you see it again and again.”

The problem is easy to diagnose, but difficult to cure, Campbell says. The competitive scramble for news, combined with the “fog of war,” combined with the absence of authoritative fact leads to defective reporting. In addition, he said, inaccurate reporting begets inaccurate reporting via what former ABC News executive Av Westin long ago termed the “Out There” syndrome — the idea that a bum fact has already been reported somewhere and is therefore fair game for others to pass on as fact.

Although good information eventually arrives to drive out the bad in a kind of journalistic Gresham’s law, bad information tends to have a pernicious effect, coloring the public’s perception of events and driving the news media’s credibility further into the ground, he said.

Campbell cites, among others, the misreporting of the aftermath of Hurricane Katrina in 2005. Many news reports suggested that displaced residents of New Orleans had descended into “Road Warrior”-style barbarism, with murder and mayhem rampant. Some of these stories were sourced, in part, to law enforcement officials, who were themselves still sorting out rumor and fact but passing on both to reporters.

In fact, there was no such crime wave in New Orleans immediately after Katrina.

While some news organizations eventually acknowledged as much, “there was no sustained look back at how to correct this kind of thing in the future,” said Campbell. “There doesn’t seem to be an ethos to correct the record.”

Investigators walk the scene of a shooting in downtown Dallas. (LM Otero/AP)

Wayward reporting has become so routine that the public-radio program “On the Media” in 2013 produced a cautionary guide to breaking news for wary news consumers.

The guide — widely shared on social media, including in the wake of the Dallas shootings — suggests that people should expect news outlets to get key details wrong in the immediate aftermath of a big event. It also recommends discounting information from anonymous sources; comparing multiple news sources; and looking for a news source close to the incident rather than a national one that is parachuting in on the story.

Its most striking piece of advice, apropos the Dallas shootings: There’s almost never a second shooter involved in any mass shooting.

The problem, says “On the Media” co-host Bob Garfield, whose newspaper column about breaking news inspired the creation of the program’s guide to the topic, is that “media [organizations] and media consumers alike can’t stand to live in a vacuum of information. They suffocate from want of detail and therefore we, and they, aren’t especially particular about where we get from.”

In an environment in which facts are scarce and even the people in charge don’t really know, Garfield encourages the media to do its due diligence and to act cautiously and responsibly. But he has no delusions about what the news media will do when the next big story breaks: “It’s foolish to blame a shark for doing what a shark always does,” he said.