First, deepest sympathies to the victims, their families and especially the loved ones of the deceased. Our deepest appreciation to all the first responders--official and unofficial--who ran into the smoke and literally bloodied their hands with their compassion for their fellow human beings. For every one villain like this in the world there are, IMO, thousands of men and women who would give their lives to prevent something like this. I try to remember that at times like this.
Nashville PD has a LTASCorp aerostat that they use for large public events. It wouldn't have hurt IMO to have extra eyes in the sky watching the crowd. The capabilities of the JIEDDO payloads are classified so we shouldn't even speculate here about any sensors that would be non-visual. My daughter has run K-9's and she and I have been talking that the devices may have been planted minutes before the explosion to avoid all the pre-event screening. Just speculation. It appears to me that someone planned this carefully and would have avoided an area monitored by an aerostat. Perhaps that deterrent value has some use, however. Clearly, Homeland Security will move up the public consciousness now. Wish it did not have to do so. Best I can do, too many bad memories, IndyJonesOhio.