Who is the red-headed man David had stopped? What happened then?

When they neared, David stepped onto the path and asked for directions to Aucharn. The red haired man, who turned out to be Red Fox/Colin Campbell, asked him why he wished to know and David intelligently explained that he was neither for or against the Highlanders but was loyal to King George. Campbell was not willing to help on this day. While he was speaking, a single shot rang out and hit Red Fox. He dropped to the ground and died. Coming to his senses, David sprang up the hill, yelling after the murderer. He continued to chase him until the murderer disappeared.