(Suburban residents) Be afraid, be very afraid
While most suburbanites believe that crime happens mostly in the city, the reality is that much crime happens in the suburbs, especially mass killings--with the exception of the recent killings at the Navy Yard in Washington, DC last fall. Mass killings tend to not happen much in big cities.
(Although it's plenty true that murder is a problem in big cities, although it is typically a function of dynamics in impoverished neighborhoods, and such neighborhoods and populations typically bear the brunt of crime, including murder.)
Today, news reports are that three people, probably including the shooter, were shot dead in a shopping mall in Columbia, Maryland, which is in Howard County, one of the wealthiest counties in the U.S.
See "Three people killed in shooting at the Columbia Mall" from the Baltimore Sun.
From the article:
Mohammed Zaidi, an 18-year-old employee of JC Penney, said customers ducked for cover after hearing gunshots. The store management then gathered people in the juniors department. "Some people were crying and really scared. I was really surprised, especially here. You don't really see that here."