The #NashvilleExplosion sounds like an offshoot of the M19 terrorist organization led by a group of Communist women
In both the #NashvilleExplosion & M19 bombs they had pre-recorded messages that gave warning to anyone in the area to evacuate (this is a very specific trademark identifiable to a group)
Left- M19 vs. Today (right)
Left- M19 vs. Today (right)