How is justice served at the end of Chapter 5?

In Chapter Five, Holmes takes down his American encyclopedia and looks under K, finding a listing for the Ku Klux Klan, a southern anti-reconstruction terrorist organization. Apparently, the KKK would often send in their threats orange pips or melon rinds or something similar. Holmes realizes that these letters must have also come from a ship given their disparate postmarks and the amount of time between the reception of the letters and the murders. Holmes, upon more investigation the next day discovers that the only ship that could house the culprits is the Lone Star from America, captained by a man named Calhoun. We can infer that justice is served when, in the end, the Lone Star was sunk at sea.