Users of 4chan had named the shooter as Geary Danley, and Google - in response to queries using Danley's name - surfaced into its "Top Stories" section a 4chan message board identifying him as the gunman. The site, which earned White House credentials under Trump, later deleted the story and apologised for the error.
Facebook's "trending topic" page also directed users towards stories by Russian propaganda websites, which cited religious affiliation as the motive behind the shooting.
In a statement shared with reporters, Google blamed the promotion of 4chan in its search results on its algorithm, which apparently is now properly tweaked.
"This should not have appeared for any queries, and we'll continue to make improvements to prevent this from happening in the future". What's become clear in recent years, on digital platforms like Google and Facebook, is that that same confusion also allows for a more nefarious dissemination of deliberately false or biased reports.
In this case, alt right websites quickly latched onto the false report for political gain, painting the falsely accused man as a Democrat opposed to the Trump Administration.
Meanwhile, Facebook's "Safety Check" page, which is created to help people near an emergency inform their loved ones that they're safe, also promoted several dubious stories from right-wing news sites Gateway Pundit and Blogspot that misidentified the suspect and his motives. "However, their removal was delayed, allowing them to be screen captured and circulated online".
The incident highlights yet again how news and social-media algorithms created to help surface the best information can fall short in the hours after a major incident, when few factual details are readily available because authorities have yet to confirm or release them.
Facebook, Google and Twitter, said they were working on fixes after learning of fake news ending up in feeds and searches following the shooting that killed 59 and injured over 500 people.
The social network said links from Web sites such as "The Gateway Pundit" and others were posted and spread across their site Sunday night.
"We are aware of this issue and are proactively taking action on content that violates our terms of service", a Twitter spokesman said. Both tech companies are facing questions about possible roles they may have inadvertently played in Russia's campaign to influence the 2016 election.