Before David Simon created The Wire he was a reporter on the Baltimore Sun, covering the crime desk. He somehow managed to convince the Baltimore PD to embed him in the homicide department for a year. Ed Burns (who co-wrote a lot of the series) used to work as a Baltimore PD detective, and the technical advisor for the first two seasons was a Baltimore police commander.

A lot of the plots on The Wire are based on actual cases and occurrences. In some cases quite loosely, in others not so much. It's a depressingly realistic show.