After their formation in 1978, M19’s tactics escalated from picketing and poster-making to robbing armored trucks and abetting prison breaks. In 1979, they helped spring explosives-builder William Morales of the Puerto Rican nationalist group FALN and Black Liberation Army organizer Assata Shakur (née Joanne Chesimard) from their respective prisons. (Both Shakur and Morales remain on the FBI’s wanted lists for terrorism and are thought to live in Cuba.)

Eventually, M19 turned to building explosives themselves. Just before 11 p.m. on November 7, 1983, they called the U.S. Capitol switchboard and warned them to evacuate the building. Ten minutes later, a bomb detonated in the building’s north wing, harming no one but blasting a 15-foot gash in a wall and causing $1 million in damage. Over the course of a 20-month span in 1983 and 1984, M19 also bombed an FBI office, the Israel Aircraft Industries building, and the South African consulate in New York, D.C.’s Fort McNair and Navy Yard (which they hit twice.) The attacks tended to follow a similar pattern: a warning call to clear the area, an explosion, a pre-recorded message to media railing against U.S. imperialism or the war machine under various organizational aliases (never using the name M19).