The Peten, Alta Verapaz, and Baja Verapaz have also seen big drops since 2010 though Peten was flat from 2011 to 2012 (maybe up 1).
Like every country, there is a great deal of variation from department to department. We'd also see similar variation within departments and cities.
Here's the data another way.
While Guatemalans tend not to perceive an improved security situation in the country, changes in the homicide rates tell a different story.