Around 1797 the brothers moved north to Kentucky, committing their first known murder along the Wilderness Road in Maryland on the way, and later killed another man, a traveler from Virginia, at a small Kentucky tavern. Identified as suspects in the murder by the innkeeper, they escaped jail and pursuit, notching at least one other murder in the process, mutilating the body and fleeing north. By 1799 Kentucky authorities had placed a bounty on each of the brothers of $300, about $5,500 in today’s money. At least five more murders were attributed to the pair as they made their way north, including three men killed in their campsite on the Saline River, for no known reason.
Cave in the Rock – also called Cave in Rock – is situated north of the Ohio River, a small village named for the unusual cave which is on a bluff above the river, easily visible from the shore on either side. Cave in Rock was the base of operations for a river pirate named Sam Mason, whose gang was known as a particularly vicious and brazen group of thieves and murderers. (Mason would later become notorious on the Natchez Trace for leaving messages to his pursuers, written in the blood of his dead victims) Since Cave in Rock was in the unincorporated Northwest Territory the Kentucky posse which had pursued the Harpes to the river had no jurisdiction and was forced to give up the chase.
At Cave in Rock, the brothers may or may not have participated in the Mason gangs’ depredations on passing riverboats. What is known is that the river pirates, hard and cruel men, found the behavior of the Harpe’s to be stunningly horrifying. The Harpes, who were still accompanied by their “wives,” raped female prisoners of all ages before killing them, usually via torture. On one occasion, the brothers escorted a prisoner to the top of Cave in Rock, above the opening of the cave, and placed him on a horse, after which they pushed all off of the bluff to fall to their deaths. The brothers were so amused by the screams that they began to make a habit of the behavior, although they stopped including horses in the crime, choosing instead to strip their prisoners naked before throwing them off the cliff.
The Mason Gang found itself unable to stomach the brother’s cruelty and shortly forced them to leave the shelter of Cave in Rock. The Kentucky posse having disbanded, the brothers re-crossed the river and eventually returned to Tennessee. Several more murders occurred in their wake, of men, boys, women, infants and in one case a whole family butchered in their sleep. Their methods included disemboweling of still-living bodies, the smashing of an infant’s skull against a tree, and cutting the throat of another infant who’s crying disturbed Big Harpe’s sleep. That murder took place in front of the mother, who was shortly murdered herself.
By late summer of 1799, the Harpe’s killing spree had led to the formation of another posse to capture them, with several of the members being relatives or friends of the pair’s victims. The Harpe’s fled to the west across Tennessee and Kentucky, wandering across the border indiscriminately.