Sometimes it is necessary that the coffin be empty because of the state of the remains.  It has happened for many years.  A World War II veteran told me that when his older brother's remains came home to South Carolina, he thought something was strange about the way the coffin was carried, so as he and another brother were "sitting up" during the night, they looked inside and found only a folded uniform.  Their conclusion then was that the body had been almost completely destroyed as his brother died. If that's the case, or if the family has chosen cremation, it's one story, but if it's for a dramatic effect, it's not good.