Three years after the riots of April 2015, the Department of Homeland Security won't say whether it was able — or if it tried — to pinpoint the origins of a "purge" flier that was a precursor to the unrest.
The origin of the notice remains unknown. It's never been revealed who first posted it on social media, or if it was widely circulated.
Shared on Instagram, the flier read, "All high schools Monday at 3 [p.m.] We Going to Purge," a reference to a movie in which there was a period of lawlessness. It called on students to go from "Mondawmin, to the Ave" — local slang for Pennsylvania Avenue — "to downtown."
Questions linger about whether the flier inspired the riots that erupted on the day of Freddie Gray's funeral, or if an anticipatory response from law enforcement essentially created a self-fulling prophecy.
Homeland Security denied a request for documents related to an investigation into the flier. In a letter, the department wrote that the Office of Intelligence and Analysis "has determined that the fact of the existence or non-existence of records pertaining to your request would be exempted from disclosure."
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Homeland Security cited an exemption that allows it to "protect intelligence sources and methods from unauthorized disclosure." The department said it was "neither confirming nor denying the existence" of records because disclosure of the records sought would "reveal law enforcement techniques or procedures and the circumstances under which those procedures or techniques were used."
Instagram, which is owned by Facebook, has not responded to questions from The Sun about whether it can trace the origins of an image. Users may search the social platform only by hashtags or location, not by image.
Emails obtained by The Sun in 2015 showed city police notified school police of the flier around noon of the day before the riots. On the day of the riots, local businesses and organizations were warned of the potential for unrest.
The Mondawmin Mall bus station and subway stop was shut down, and police officers in tactical gear set up in the area.
City and transit authorities have never identified who or what agency made the call to shut down the station. The Mondawmin station is a crucial transportation hub that students use to get home from school. Some have said the students reacted to the heavy police presence and the lack of options for leaving.
Documents obtained by the ACLU in 2016 show that the social media company Geofeedia had been monitoring social media chatter about a planned protest. The civil liberties organization also obtained a Geofeedia "case study" in which it said its social media surveillance captured chatter for a local school about kids planning to head to the Mondawmin protest. It cited a Baltimore County police intelligence sergeant as saying police then "intercepted the kids — some of whom had already hijacked a metro bus — and found their backpacks full of rocks, bottles and fence posts."
Young people and police clashed at Mondawmin. Then a large group of young people made their way to Pennsylvania Avenue. A CVS store was set on fire and looted. Similar looting broke out across the city.
The Maryland Transit Administration, which operates the Mondawmin station and its camera system, has refused to release any of the footage. The Baltimore Sun, city officials, activists and others have asked questions about the role the MTA and the city police department might have played in escalating the tensions.

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The MTA said releasing the footage would present unacceptable security risks by divulging where cameras are located and how they pan and zoom.
The flier's origin remains a mystery.
In a federal indictment released in February, Special Counsel Robert Mueller said Russians used social media to sow discord, including with an account named "Blacktivist" that reached out to Baltimore activists and media after the riots seeking to promote more protests.
The FBI's Baltimore field office said it "did not look into Purge meme."
"We were aware of it at the time, but the FBI did not look into where it came from," said David Fitz, a spokesman for the office.