The cameras were on the cart 10 feet away from the door. The guard was down at the other end of the 250’ hall. The cameras detected the guard, the shooter sprays the hall quite possibly taking out the cameras so he could have blinded himself in the process. We still don’t know how far down the guard was when the spraying started.
It was reported at one time the cops got the guard back to the elevator vestibule.
You are only guessing at circumstances that fit the narrative.
What you are saying is possible, but so are a lot of other scenarios.