Diver: Sotai Sennyuuhan

To fight gang-related crime, the police created the Divers: investigators who have infiltrated the highest levels of the mafia. Hyougo Kurosawa, considered the best Diver because he is the worst of the worst police officers, infiltrates Team A, a gang of extremely intelligent crooks from top schools who ruin elderly people through bank transfer scams.

(Source: Shueisha, translated)