Just an observation:
The posted hazmat sign indicates the 'bomb' (exactly like the one you describe) was already there...
View attachment 278676
See: Google Maps @ 172 2nd Ave N. Nashville:
(yes, the very front of the AT&T building is blurred, but scoot just to your left, above the head of the person on the street).
I can't be the only person who has seen this. Why is is not part of the "investigation?"
This type of hazardous material sign is not unusual for network and data centers. Generally, the warnings are related to power systems, particularly fo large DC power plants utilizing sizable battery plants, and fire suppression systems. IMO, the site has been combed through for evidence and if there's anything to this it will be part of the investigation.