What changes Jasper's actions as a vampire?

One day while Jasper was supposed to be killing the newborns under orders from the woman, another vampire who had fought beside him begged him not to. The vampire ran away with one of the newborns scheduled for termination. Sometime later, having grown unhappy with his lifestyle, this same runaway vampire told Jasper that things were different in the north. Jasper left his army and traveled to the north where he eventually met Alice and learned about the Cullens.