 He is based on Baltimore Police Department Shift Lieutenant Gary D'Addario, a member of the BPD homicide unit described in David Simon's book "" which served as the inspiration for the series as a whole.The character also appeared in the "Law & Order" episode "Baby, It's You".Al Giardello – nicknamed "Gee" after the only thing he could say when called to his first murder scene as a rookie as well as a reference to his last name – is the commander of the Homicide unit shift followed by the series.