We came to this house to try to understand the forces of social disruption that have followed Facebook’s rapid expansion in the developing world, whose markets represent the company’s financial future. For months, we had been tracking riots and lynchings around the world linked to misinformation and hate speech on Facebook, which pushes whatever content keeps users on the site longest — a potentially damaging practice in countries with weak institutions.

Time and again, communal hatreds overrun the newsfeed — the primary portal for news and information for many users — unchecked as local media are displaced by Facebook and governments find themselves with little leverage over the company. Some users, energized by hate speech and misinformation, plot real-world attacks.

A reconstruction of Sri Lanka’s descent into violence, based on interviews with officials, victims and ordinary users caught up in online anger, found that Facebook’s newsfeed played a central role in nearly every step from rumor to killing. Facebook officials, they say, ignored repeated warnings of the potential for violence, resisting pressure to hire moderators or establish emergency points of contact.