"There were stories about the alleged shooter that misidentified," Roose told Early Edition host Rick Cluff. Roose called it "a grab bag of misinformation, hoaxes, conspiracy theories and actually propaganda."
In a statement, Google explained it was "briefly surfacing an inaccurate 4chan website in our search results." 4Chan is an online messaging board with a far-right contingent.
Facebook, which created a crisis page on its platform to allow users to notify friends they were safe, similarly shared links with inaccurate information.
Roose says it's the responsibility of companies like Google and Facebook to ensure the information posted on their platforms is accurate.
Both Facebook and Google said in statements they are working to fix problems with their algorithms that choose their top news stories.
Roose points to these companies seeing themselves as technology platforms and not media organizations as a reason for their lack of accuracy. Both platforms rely on algorithms instead of human editorial judgment to determine what is accurate and what is trending.
However, Roose says if online platforms begin to identify more as news outlets and allow for more editorial judgment, they could open themselves up to a lot more criticism.
"It's risky for them to determine which news organizations are putting out real and fake news. They don't want to be seen as partisan," said Roose.
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With files from The Early Edition.