Even though it still ranks second on the most dangerous cities list, St. Louis is a lot safer than it used to be. Murders have been cut in half over the past two decades -- as have the numbers for other violent crimes.

Still, at about 35 murders per 100,000 residents in 2011, St. Louis claims the third highest homicide rate of any major city.

One reason St. Louis's crime rate is so high is that the city has not grown beyond its very constricted borders, according to criminologist Richard Rosenfeld of the University of Missouri, St. Louis. Other cities have expanded outward by swallowing up safer nearby communities, which helps dilute the overall crime stats. Oklahoma City's reporting area, for example, is nearly 10 times the size of St. Louis'.

If the safer St. Louis suburbs were counted into its crime statistics, the overall crime rate for St. Louis would be much lower.