According to a report from the Commons Intelligence and Security Committee, the 2013 murder of British soldier Lee Rigby might have been prevented if Facebook had flagged the graphic messages posted by the two extremists who murdered him in the days leading up to the attack.

The report said that Michael Adebowale, one of the attackers, had posted on Facebook about killing a soldier before the attack, though the message wasn’t found until afterward.

“Had MI5 had access to this exchange at the time, Adebowale would have become a top priority,” the report said. “There is then a significant possibility that MI5 would have been able to prevent the attack.”

However, the report didn’t stop there. The members of parliament responsible for the investigation explicitly called out Facebook for its lack of action, and even accused them of harboring terrorists.

“This company does not regard themselves as under any obligation to ensure that they identify such threats, or to report them to the authorities,” the MPs said. “We find this unacceptable: however unintentionally, they are providing a safe haven for terrorists.”

While Facebook tries its best to police itself, the site is simply too big to catch every potentially dangerous thing that’s said on its pages. However, this issue could drive an even bigger wedge between Facebook and European nations, many of which already distrust Facebook over its privacy practices.