The following is taken from pages 170 to 171 of Henry Plummer: Lawman and Outlaw

By late summer Virginia City had become the business center of the territory. Bannack, with a loss in population and business, found the sheriff's office involved in sheriff's sales for those who wanted to dispose of mining claims and possessions prior to leaving the town. Among the latter was Peter Horan who wanted to sell his interest in a mining claim owned jointly with Laurence Keeley. Prior to the time that Horan called on Plummer in regard to holding the sale, there had been some difficulty between Horan and his partner. The sale held on the afternoon of Friday, August 14th, brought $500.00, far less than Horan had expected. There is some reason to believe that Keeley had bought Horan's interest or had a third party buy it for him. In any event, Horan blamed Keeley for the low price that he had received and threatened to even the score. Using some of the money, Horan bought a horse and kept it at a corral at the edge of town with the stated intention of leaving the country. At five o'clock on the morning of August 19th he knocked on Keeley's door, saying that it was important that he talk to him. As Keeley opened the door, he was shot at close range and dropped to the floor. As a final gesture, Horan stepped in the doorway and fired several more shots into the body. The sound of the firing had aroused several nearby residents and Horan was captured at the corral before he could leave town.

At nine thirty on the morning of the 19th, a coroner's jury was called into session to consider the evidence in the death of Laurence Keeley. The facts as presented left little doubt that Peter Horan was guilty of premeditated murder, and was sentenced to death. That same afternoon Horan was taken to the scaffold that Sheriff Plummer had hastily constructed by nailing a crosspiece across the top of two pine trees only hours before. One writer, acquainted with early day residents of Bannack, claimed that Horan was under the influence of a drug and in a semi-conscious condition at the time he was hung. Another story that was told claimed that to save time and space both Horan and his victim were buried in the same grave. A map of early day Bannack reveals that the Plummer cabin was in plain view of the scaffold and the young wife of Plummer could watch the execution if she so desired, which is doubtful. In any event, it was soon after this, on September 2nd, that Electa Plummer left Bannack on a stage bound for Salt Lake, in route to her parents at Cedar Rapids, Iowa. Plummer was said to have accompanied the stage as far as the Snake River crossing before turning back. He would never see his wife again.

Dimsdale in Vigilantes of Montana, in Chapter XXVII mentions Horan in passing. He is describing the hanging of the last of the vigilante victims in Bannack, whom he calls Rawley, but Amede Bessette who knew him and believed him innocent, spelled his name Rawleigh. Dimsdale says

he was hanged on the same gallows which Plummer himself had built for the execution of his own accomplice, Horan, and on which he himself had suffered.