There needs to be a thorough public investigation. Why was a roof within 150 meters of the stage not included in the security perimeter? It seems to me that there only 2 possibilities, either something nefarious or gross incompetence.

Moreover, any investigation needs to be absolutely transparent and the report needs to make rational sense. We don't need something that has the appearance of a Warren Commission style coverup or any crazy Arlen Specter style magic bullet theories.