Below is an article on the Virginia Beach mass murder and about use of the shooter’s suppressor. Earlier reports I read quoted people in the building saying they “heard the shooting” and barricaded themselves in their offices. The killer was reported to have had two weapons, so it is possible one had a suppressor and the other not such that the non-suppressed weapon was being heard. We will have to wait for further info on what happened and the big “why” this guy went bezerk.

https://www.haaretz.com/us-news/did-...nage-1.7314182

As Mike says, the action of the gun and the shell casings dropping are a give away to knowledgable folks.