Beginning midway through 2011, the Baltimore State’s Attorney’s Office, for the first time in modern history, became the sole arbiter of when to charge a defendant in a homicide investigation. Previously, that decision rested with the police department, which would do so in consultation with prosecutors from the Violent Crimes Unit of the State’s Attorney’s Office. Which is to say, while police detectives were expected to take guidance from prosecutors — and did so — they were nonetheless free to arrest defendants if they felt the evidence warranted a charge.
Mr. Simon gets a bit wordy here, but it really does explain a few things. Read it, if you've got the time.