You do not know that they were black sweatshirts.
They have not been identified.
Except for one person claiming they were black sweatshirts. They are large items. That are black.
One eye witness does not mean it is true- especially that one.
How is it that she didn’t see any cop cars, fire engines, police or anything as she stood at that door.
Because the first police on the scene parked their cars neatly between the lines in the parking lot and they blended in with the other cars. Check the aerial video. Unless you were looking for them you wouldn't notice them.