A retired top policeman helped Robert Menendez’s wife-to-be leave the scene of her fatal car crash without a sobriety test or handing over her phone. The Post has learned that Michael Mordaga, the former director of Hackensack police and an ex-chief of detectives in the Bergen County Prosecutor’s Office, was on the scene within minutes when Nadine Arslanian slammed her black Mercedes into Richard Koop in Bogota, NJ, in December 2018. Mordaga, 66, helped her leave behind the totaled car and take her belongings from it after quizzing the patrolman dealing with the crash on what he planned to do....