Check out the these previous answers on violence in the Wild West, along with the related FAQ section:
Was being a Sheriff in the wild West a coveted position? by /u/itsallfolklore
How violent was the Wild West? and How accurate is Hollywood's portrayal of what we know as "The Wild West"? by /u/petite-acorn
How common were train robberies in the American West during the time of massive railroad expansion and how did they happen? by /u/nilhaus