 Complete the following phrase:  But two months later on December 28, friends of the slain outlaws retaliated, ambushing Virgil. They shot him in the back, hitting him with three shotgun rounds, shattering his left arm and leaving him permanently maimed. The Cowboys suspected were let off for lack of evidence. His brother Morgan Earp was assassinated in March 1882. Charges against those suspected were dismissed on a technicality. Wyatt Earp, appointed as deputy U.S. Marshal to replace Virgil, concluded he could not rely on civil justice and decided to take matters into his own hands. Wyatt assembled a federal posse that included their brother Warren Earp and set out on a 