Joy Postell was living in Los Angeles when the news broke of Freddie Gray’s death in her hometown, Baltimore, on April 19, 2015.

“I was in a state of panic,” Ms. Postell said. The story had been unfolding in real time for days, since initial reports that the 25-year-old Mr. Gray had been arrested, on April 12, and in the course of a 45-minute police van ride, sustained a spinal injury that left him in a coma.

On social media, Ms. Postell saw that her city had erupted in protests against police brutality. She wanted her pain and frustration to be heard, too, even if from a distance.