Why did Openshaw's uncle return to Europe in "The Five Orange Pips"?

In the Sherlock Holmes story "The Five Orange Pips" by Arthur Conan Doyle, a man named John Openshaw comes to Holmes and Watson because his uncle Elias Openshaw was murdered, and he now considers his own life in danger. He says that his uncle Elias had emigrated to America and had become a planter in Florida. During the American Civil War, he served in the Confederate army. A few years after the war, he returned to Europe and took a small estate in Sussex. The reason Elias gave to his nephew was "his aversion to the Negroes, and his dislike of the Republican Party in extending the franchise to them." In other words, he didn't like the recently-freed African Americans and the government that had freed them.
During the course of the story and the investigation by Holmes, this proves to be an excuse and is not the real reason that Elias Openshaw returned to England. In fact, Elias fled the United States because he had taken a register and diary from the Ku Klux Klan. Former members of the Klan were concerned that these papers would implicate them in crimes, and so Elias was afraid that they would come after him. The five orange pips are a message that Klan assassins send to their victims that they are about to be killed.
Eventually, the assassins catch up with John Openshaw and kill him too. Sherlock Holmes discovers the ship that the killers are on and plans to have them arrested. However, the ship is lost at sea and never reaches port.