Inside the groundbreaking science used to identify 9/11 remains

The north tower was already billowing smoke when Mark Desire, then a 33-year-old criminalist with the city Office of the Chief Medical Examiner, made it to Ground Zero to assess the dead. Instead, he nearly joined them. Desire had just received marching orders from the chief medical examiner when Flight 175 smashed into the south tower overhead, showering him with deadly debris.