The three experts of the United Nations fact-finding mission on Myanmar, who also addressed the human rights council about their ongoing investigation, were equally forthright in their condemnation.
U.N. Myanmar investigator Yanghee Lee said Facebook was a huge part of public, civil and private life, and the government used it to disseminate information to the public.
The UN has been denied access to Rahkine since late previous year, so both Yee and the fact-finding mission have been forced to conduct their investigations in Cox's Bazaar in Bangladesh, where hundreds of thousands of Rohingya are now living in refugee camps.
Almost 700,000 Rohingya Muslims have fled northern Rakhine state to Bangladesh since Myanmar launched a brutal crackdown on insurgents six months ago amid accounts of arson, murder and rape at the hands of soldiers and vigilante mobs in the mainly Buddhist country.
Chair of the fact-finding mission, Marzuki Darusman, the former Indonesian attorney general, said the Myanmar government's continued denial of any culpability for the violence in Rahkine was "untenable".More news: Trey Burton expected to sign with Chicago Bears
The evidence they had collected "points at human rights violations of the most serious kind, in all likelihood amounting to crimes under global law".
He said: "What I have heard and witnessed in Cox's Bazaar is a human tragedy with the fingerprints of the Myanmar government and of the global community".
UN Myanmar investigator Yanghee Lee said that "everything is done through Facebook in Myanmar", adding it has been used to spread hate speech. Because of that, it's been easy for ultra-nationalists to use the platform to stoke hatred against the Rohingya minority, who have been targeted by government forces, killed by the thousands and driven out of the country.
Lee told the Human Rights Council that violent sweeps by the Myanmar army in Rakhine state that prompted about 700,000 Rohingya Muslims to flee to neighboring Bangladesh "bear the hallmarks of genocide".
"I'm afraid that Facebook has now turned into a beast, and not what it originally intended", she said. Beyond its global effort to bolster its content moderation by hiring more reviewers, it says it routinely removes hate speech content in the country, including Wirathu's account (although this only happened in late February), and that it has developed and promoted localized guidelines for using Facebook.