A Washington Post analysis of police data shows that half of the 55,000 homicides in 55 U.S. cities over the past decade did not result in an arrest. Shown below are the 10 cities with the highest homicides totals in the years studied. Philadelphia had the second-highest number of homicides, but also the second-lowest percentage without an arrest, trailing only Memphis. New York City is not on this list because its police department only supplied the Post with two years of data.