The movement began on social media. In July 2013, George Zimmerman was acquitted of murdering Trayvon Martin, an unarmed black teen shot to death during a struggle in a gated community in Sanford, Fla. Garza, an activist with the National Domestic Workers Alliance in Oakland, Calif., was sitting in a bar when the verdict came down. She posted a missive on Facebook, punctuated by a powerful "Black people. I love you. I love us. Our lives matter." Her friend Patrisse Cullors, another veteran California activist, who founded the prison-reform organization Dignity & Power Now, replied with a message that included the hashtag #blacklivesmatter. It gained a modest foothold in the year after Zimmerman's acquittal. But after Michael Brown's death, the hashtag became a rallying cry. On the November day a St. Louis grand jury declined to indict Darren Wilson, the Ferguson cop who shot Brown, the hashtag was used 202,492 times. These are Top Stories from TIME explore #BlackLivesMatter.