The episodes leading up to Langer getting shot, it appears he is new to NCIS, but prior episode it turns out he started out under Gibbs, then went to FBI. Now back? What gives?

He worked with Gibbs and Fornell on a case, he was still an FBI agent at that time, had been for 10 या so years before he became an एन सी आइ एस#Naval Criminal Investigative Service agent in season 6. Hope that helps