There are videos of the flashes on the fourth floor from 1-2 hours before the shooting started.
>>There are videos of the flashes on the fourth floor from 1-2 hours before the shooting started.
Not surprising. Looks like a reflection of a billboard or something to me. Or maybe the screen/lighting at the concert.
Good observation.
Another video just posted here clearly shows strobe light around 4th floor going well before any shooting.