While traveling with her master, Mr. Wheeler, they happened to stop in Philadelphia. By Pennsylvania law, any slave brought into the state was free should they wish to be, just by crossing the border. While locked in a hotel room, Johnson was able to get word to the Pennsylvania Anti-Slavery Society that she wished her freedom. William Still and Passmore Williamson were able to catch her before she left Pennsylvania, at the Philadelphia docks. William Still escorted her off the boat and Passmore Williamson explained the situation to her master. As a result, Passmore Williamson spent 100 days in the Moyamensing Prison.