Following a police shooting in northern Brazil, people started getting messages. On WhatsApp, they were warned to stay indoors that night. Some of the WhatsApp messages were texts, though the most popular was an audio file with a dire warning: "Don't go to Guama, Canudos or Terra Firme tonight. It concerns your security," it said, according to the BBC. "One of our policemen was killed and we will be cleaning the area."
The next morning, ten people were dead, killed on the streets. People used the #ChacinaEmBelem hashtag to document the dead bodies still laying there, and to discuss theories about what went down. Most suspected off-duty cops, since the slaying looked like it was retribution for the police officer shot dead. But no one was arrested, and the messages haven't been traced back to anyone.
The Belem murders are not unheard of for the area, but this type of warning is. "These kinds of retribution and extrajudicial killings are very common, not just in Belem, but also in São Paulo and Rio de Janeiro," Graham Deyner Willis, a Cambridge lecturer writing a book about violence and consensual governance of urban space in São Paulo, told me.
In recent years, social media has played an increasingly larger role in documenting the blood and gore of street violence, including killings from police and organised crime. You can find videos on Facebook that police took, showing people they just shot (warning: that links to graphic video). You can find all sorts of videos showing police gunning people down and organised crime factions shooting at each other (again, warning, those links bring up disturbing stuff).
"The case with WhatsApp in Belem is a little bit different, because it is as though the perpetrators were signalling to a community of people that they didn't want to kill to stay off the streets," Willis told me, pointing out they also spread warnings on Facebook.
What went down in Brazil is new because this is the first time people have circulated messages on WhatsApp before they committed a violent act in order to protect who they saw as innocent. But using social media as an immediate tool for communicating in conflict is not new at all. People living in armed-conflict situations often post about their lives and use social media as a news source. That's not a Brazil thing. That's an everywhere thing: Think of how people take to Twitter to report on the Boston Marathon bombing.
Of course it's a jump to go from using social media to document violence to using social media to try to control it. These killers can't finesse the trajectory of their bullets, but if they're going to shoot guns, they're trying to keep innocents out of the way. It's a sort of bullshit robber honour that almost looks thoughtful if you set aside that they could also just not go on vicious murder rampages instead of trying to minimize the bloodshed caused by their vicious murder rampages. And if you also set aside messages like this can incite widespread panic.
This is the flip side of social media getting used to spread severe weather warnings and Amber Alerts, with criminals using services to circulate their own advisories. If this kind of thing becomes more commonplace, it will be difficult to stop but also negligent if the services turn a blind eye.