In an interview with the New York Post, Anderson said that Bernard is "a former IAB [internal affairs] officer who didn't sign up for that job - they recruited him right out of the academy and told him he could become a homicide detective in two years. It's what he really wants to do. Bernard feels he can really make a difference as a homicide detective."
His first day on the job will be in the April 23rd episode, which is also the last one for Detective Ed Green, a member of the TV Crossover Hall of Fame played by Jesse L. Martin.
"He's not a hard-ass," Anderson said in describing his character. "He's a fair guy trying to find his way in a new station house - and trying to get away from the stench of the 'rat squad' of internal affairs."
That may be how he's brought in to the show and Detective Green is taken out. It's been awhile since one of the cops left the 2-7 in disgrace. (That would be Detective Tony Profaci in the related TV movie, "Exiled".)
But there's no use speculating, since we'll have the answer in a couple of weeks....
[Detective Bernard is pictured here with Lt. Anita Van Buren, another Hall of Fame member who is in charge of that shift at the 27th Precinct.]