Off-duty NYPD cop stabbed in mugging reveals why he fought to keep necklace — and how thugs reacted when he told them he was police

The off-duty NYPD cop stabbed in a mugging revealed Tuesday that he fought back as his attackers grabbed the gold chain his mom gave  him — adding the thugs didn’t care when he told them he was police. “I almost died,’’ said Detective Jose Mercedes, speaking for the first time since the bloody Oct.