The amateur investigators who frequent 4chan's /pol (short for "politically incorrect") discussion board identified a man named Geary Danley as the shooter-a claim that was incorrect and based on primarily on political motivations rather than factual information.
They were shocking, gruesome revelations.
Meanwhile, Facebook's "Security Check" page - that lets people involved with disasters and accidents post messages for friends and loved ones - published a blog post from "Alt-Right News" that said "the killer may have been a Trump-hating American television host Rachel Maddow fan" in an apparent reference to the misidentified Danley's Facebook page. The most egregious example has got to be the story which claimed that the shooter was an anti-Trump Democrat.
Google and Facebook blamed algorithm errors for these.
"It would have had to appear in any search results and we will proceed with further improvements to prevent this from happening again in the future", added the group which has built its success on its search engine.
But this was no one-off incident.
Google and other tech giants like Facebook have prided themselves on their commitment to eradicating "fake news".
Facebook on Monday turned over to Congress 3,000 ads linked to a Russian troll farm.
Platforms 4chan, and Atms are among the most popular. These companies rely on promoting content they think people will click on.
On Facebook and Twitter, where tweets claiming to be urgent messages about missing loved ones ran rampant, fake information can be even more hard to discern as the posts mirror legitimate cries for help. Similarly, according to a Buzzfeed report, even Twitter might be one of the places where fake news might have found a way to be spread.
There is also a labeling issue.
Fake news stories spread on social media in the hours after the mass shooting in Las Vegas as people looking for information read and shared bogus reports and hoaxes without even realizing it. Voila. Problem solved; case closed. But fixes that require identifying "reputable" news organizations are inherently risky because they open companies up to accusations of favoritism.
In a statement to CBS News, Facebook said the Vegas false news issue has been fixed and it's focused on a long-term solution: "We know people want to see accurate information on Facebook - and so do we".
But just because the war against misinformation may be unwinnable doesn't mean it should be avoided.
Among those falsely stated to be missing in Las Vegas were a German pro-soccer player, a murder suspect from Mexico and a male porn star - whose pictures were taken from the Internet.
Kevin Roose is a business columnist for The New York Times and a contributor to The New York Times Magazine.
Facebook and Google have spent billions of dollars developing virtual reality systems.