Drew Crowley was formerly a San Diego policeman and the brother of Detective Terry Crowley.
Nothing is known about Drew Crowley's early life, other than that Drew's father was a policeman and he eventually became a policeman like his father and his brother Terry, who worked as a detective and as a member of the Strike Team in the Farmington District in Los Angeles, while Drew worked as a cop in San Diego.
In season 5, IAD Lieutenant Jon Kavanaugh made it his personal mission to arrest and sent to prison Vic Mackey, whom he believed had killed Terry. Kavanaugh tried his best to catch Mackey red-handed and tried to force confessions out of him and Detective Shane Vendrell, who was also part of the murder plot. Eventually, Kavanaugh forced Mackey and Vendrell to revisit the crime scene where Terry was killed and to say exactly what happened that night in details. Drew also appeared, having been brought by Kavanaugh to face the his brother's killers. At this time, it is also revealed that Drew left the force after his brother's death. Kavanaugh introduced Vic to Drew, who says: "He doesn't remember 'cause he never looked at me or my family that day (Terry's funeral)". Drew correctly assumes that Vic murdered his brother and repeatedly asked him what happened to his brother. Sensing that things are getting out of hand, Kavanaugh orders that Drew be taken away. While being led out, Drew exclaimed: "If you're lying, God will have your soul- and I will give it to him personally." Vic and Shane stick to their original story and Drew is not seen again.