Australia's internet regulator says X refused to take down a video of a high-profile stabbing in Sydney that was watched by Axel Rudakubana just before he murdered three young girls in Southport.
The body, eSafety, said it "noted with great sadness" that Rudakubana viewed the violent footage of the attempted murder of Bishop Mar Mari Emmanuel.
It said other major tech firms complied with its request to take the video down, but X - owned by Elon Musk - only blocked it in Australia, meaning Rudakubana was able to view it minutes before leaving his home to carry out his deadly attack.
The 18-year-old has been sentenced to a minimum of 52 years for the murders.
X has been contacted for comment.
