In the hours after last Sunday's shooting at a Quebec City mosque that left six worshippers dead, journalists did what journalists do: try to learn details about the people involved.

By the next morning, several news outlets, including CBC News, were quoting unnamed police sources who said two suspects were in custody.

According to Brooke Gladstone, host and managing editor of a U.S. radio program on WNYC called On The Media, that should have been the first clue that the information would ultimately turn out to be wrong.

The Investigators with Diana Swain airs at 9:30 p.m. ET Saturday and 5:30 p.m. ET Sunday on CBC News Network.

She spoke to CBC's The Investigators this week from her home in New York City.

Police officers patrol the scene of a fatal shooting at the Quebec Islamic Cultural Centre in Quebec City on Jan. 30, 2017. In the aftermath of the attack, police arrested two men, but only one was charged. (Mathieu Belanger/Reuters)

"There almost is never a second shooter," says Gladstone, who has written what she calls a "Breaking News Consumers' Handbook" — a list of nine tips that the public can use to comb through the facts, some of which are often wrongly reported, in the immediate aftermath of a breaking news story.

"If you avoid almost anything that quotes an anonymous source — whether it's an anonymous police source, or a political source, or an FBI source — anonymous sources generally indicate that people aren't standing by their impressions."

Brooke Gladstone is the host and managing editor of U.S. radio program, On The Media, which looks at how the media can shape world views. (Provided)

While two men were initially arrested in the aftermath of the mosque attack, one was later released when police determined he had nothing to do with the shooting. He had run from police at the scene, causing them to believe he was involved — but having escaped the mass shooting inside, he told them he simply ran when he saw someone come toward him with a gun. It turned out to be an officer with his weapon drawn.

Even the man's surname as initially reported was wrong. Once police clarified that he was no longer a suspect, but rather a witness to a terrible crime, most media, including CBC News, quickly reported that fact.

Fluid situations

Gladstone says she wrote her "handbook" after the fatal 2013 mass shooting inside the Washington Navy Yard. Washington's police chief initially announced they were looking for two shooters. It turned out only one man, Aaron Alexis, was involved. Thirteen people were killed, including Alexis, who was shot dead by police.

Gladstone and her team have since written similar handbooks on specific breaking news themes, such as coverage after a natural disaster or after a plane crash. She says the guides have "been downloaded millions of times all over the world. Because it seems that the way we screw up the news here [in the U.S.] is pretty much how everyone screws up the news everywhere."

A bullet is lodged in a column inside the Quebec City mosque where six people were shot and killed Sunday. (Alice Cliche/Radio-Canada)

But names and the number of victims are frequently corrected after the initial coverage, she says.

The handbook isn't intended to make people turn away from breaking news, she says, acknowledging that people usually want to know what's happening, while it's happening.

Instead, it's about watching with the understanding that fluid situations mean information can change.

"It's really just in the moment — or in the very, very short after-moments — that things tend to be wrong."

Also airing this week on The Investigators: CBC News reporter Curt Petrovich talks about his struggle with PTSD and why he's decided to go public with his private torment.