Pity

The truth is, the moment he saw Leon kill that rattlesnake earlier, he already knew that he was in deep trouble. 

That's why he immediately sent out a distress signal towards his companions in the city to request for reinforcement. 

Not only to save himself but to also have the opportunity to kill Leon. He was really a troublesome fellow and he knew that he would surely hinder their plan in the future. 

That method to send a distress signal was unique to him and his companion. The Adventurers Badge of the Adventurers Guild also has the same function but the message would only be delivered to the Guild Master himself. 

Unlike the Dark Stone in his possession, it could be used to send a distress message towards a single individual as long as they were inside or not far away from the city. It also has a tracker so he does not have to worry about not being located by his companions.