In 1988, for example, there were 234 homicides in Baltimore. Tracking all of those cases, a reporter would learn that 22 of them were cleared by the police department through arrest, but then later dropped by the state’s attorney’s office prior to indictment. What did that mean to the police department? To the prosecutor’s office? To the city of Baltimore?
Well, for the police department it meant credit for solving 22 cases that they didn’t actually solve, given that the evidence was insufficient for prosecutors to obtain even a grand jury indictment. Why? Because the FBI’s crime reporting logic allows police departments to take credit for all cases cleared by arrest, regardless of whether those arrests are any good at all. Once an arrest has been made — even if charges are subsequently dropped — the case is credited as cleared, and its status as a cleared case doesn’t change.
For the Baltimore state’s attorney’s office, there was no institutional cost to be paid for these 22 weak sisters. Why not? Because the State’s Attorney only computes his overall conviction rate — a statistic that he will run on for reelection every four years — using cases that have been indicted by a grand jury. Cases dismissed prior to indictment don’t count against him either."
— David Simon, Dirt Under the Rug; Know what your numbers tell you and what they don’t tell you.