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Many New York City detectives take great care in selecting their professional wardrobes, from the necktie and pocket square to the wingtips. They buy specially tailored coats to conceal a sidearm on the hip, with a little extra give in the sleeves to accommodate a shooting stance.

But one part of the uniform is seemingly optional, worn only on certain occasions — and yet, it is the one that is intended to save a detective’s life. A bulletproof vest.

The Police Department’s Patrol Guide dictates that detectives must wear the vest when performing enforcement duty, such as making an arrest. Other times, it is up to the detective.

The stakes behind that decision came tragically to the forefront last month, when Detective Brian Simonsen, responding to a call of a robbery at a cellphone store, was fatally shot in the chest in police crossfire. He had sped to the scene from an unrelated surveillance operation, dressed in business attire, and had not been wearing a bulletproof vest.