A “Las Vegas shooting” search on the Google-owned platform led users to numerous videos questioning whether the government was lying about the basic facts of the tragedy and suggesting victims could be “actors”.

On Wednesday a YouTube spokesperson insisted that the site was highlighting reputable videos and the conspiracy videos on its search page did not violate its standards. But less than 24 hours later the company altered its position, implementing changes to its platform in a direct effort to better promote reputable sources.

A YouTube source confirmed on Thursday that the company tweaked its search algorithms late on Wednesday night, hours after survivors and victims’ relatives criticised the company for prominently featuring videos with hoax claims. YouTube had been working on this change for months and decided to push it out early this week, the source said. It is unclear how the new algorithm functions or whether it is effective in downgrading falsified accounts of the attack.

YouTube declined to answer questions about the changes, which were first reported in The Wall Street Journal.

YouTube’s initial statements, followed by its readjusted algorithms, speak to the broader ethical challenges technology companies face regarding their role in providing major platforms for fake news and propaganda. Facebook and Google were both caught promoting rightwing blogs and conspiracy sites hours after the Las Vegas shooting, forcing the corporations to admit that they had made mistakes in spreading misinformation about the identity of the shooter.

Silicon Valley has faced heightened scrutiny over the last year for allowing political propaganda and fake news to reach wide audiences, possibly playing a part in Russia’s efforts to interfere with the US presidential election.

Conspiracy theorists regularly spread unsubstantiated “false flag” conspiracy theories after mass shootings in the US, sometimes leading to real-world harassment and bullying of victims and survivors. But some fear that YouTube and other social media sites have amplified the problem by connecting people who believe tragedies are staged and actively presenting them with similar content that confirms their suspicions.

A “Las Vegas shooting” search on Thursday, after the algorithmic change had taken place, produced substantially more reputable videos, mostly from mainstream news sources. One conspiracy video still featured prominently, however, along with a warning from the creator of the clip that YouTube was trying to censor it. It later disappeared.

Beyond the search page, it was unclear if any conspiracy videos had been taken down altogether; at least some short films that argued the shooting may not have happened at all remained active on YouTube, rapidly garnering hundreds of thousands of views. Next to these videos, YouTube also continued to promote related content with blatant propaganda and false news.

That included: “CNN Crisis Actor Caught Red Handed” (450,000 views), “Government Staged Las Vegas Mass Shooting” (300,000 views) and “Las Vegas Shooter At Mandalay Bay Hotel Part Of FBI Undercover Sting Operation” (400,000 views).

Stephen Melanson, whose wife and daughter were both shot in the attack, said earlier he believed YouTube should remove footage suggesting the deadliest mass shooting in modern US history wasn’t real.

“When I see my wife fighting for her life with a gunshot wound to her chest, and my daughter was also shot, it’s pretty conclusive evidence that it did happen.”