Fred Gray, 87, bespectacled and a bit hard of hearing, stood quietly over the archival box. His hands, though, were a twitching blur: flipping past some folders, opening others, rustling through records that dated back more than half a century.

“Some of these,” said Mr. Gray, who was a young lawyer during the height of the civil rights movement, “I’ve never seen.”

Here was an arrest warrant declaring that Rosa Parks, a client, “did refuse to take a seat assigned to her race.” ​Here was an appeal bond for the Rev. Dr. Martin Luther King Jr., another client.