Which windows were open as the shots were being fired?
The two-story AGR building directly behind the one that the assassin, Thomas Crooks, fired from, initially contained three Emergency Services Unit (ESU) Snipers. One from Butler County ESU and two from Beaver County ESU. Butler County was in charge.
They had been told to keep the windows closed, however it was a very hot day. The following image was taken inside one of the AGR buildings in the aftermath of the shooting and shows only a single air vent in the ceiling, so there may not have been air-conditioning available throughout most of the buildings.
The video from Piper Grimly.
The following video records all the shots being fired whilst the person filming moves across the side of the building and just makes it around the corner, briefly showing the front of the building.
It is remarkable in that it absolutely proves which windows of interest were open as the shots rang out.
The side window was open as the shots were being fired. This is probably the window that photos were taken earlier in the day by one of the Beaver County ESU snipers of Crooks sitting near the corner of the building holding a rangefinder.
The Shooting continues
NIX Detail Enhancer was used to make the open windows more visible.
This is the most important image from the video. Here we can see two windows clearly open as the shooting was happening. There are another two windows in the middle of this image hidden by the ducting.
Of the three ESU snipers, one had ended his shift and gone home mid-afternoon, and another had gone downstairs, exiting the building to look for Crooks shortly before the shooting started.
The remaining sniper, from Butler County ESU, was stationed alone at the leftmost open window in the above image. His sniper weapon was mounted on a tripod and had camouflage netting over it.
This image was likely taken earlier in the day.
As an aside, it is possible to determine the status of the two windows that weren’t visible in the earlier image
Taken some minutes after shooting, this image shows ESU members on the roof next to Crooks. The bodycam briefly captures a view of the second floor.
Zooming in, we can see that of the two windows not visible in the earlier image, the one closest to the ducting is open. Note: This is some minutes after the shooting finished.
The leftmost and rightmost windows were definitely open during the shooting. The middle one was open by the time the ESU personnel made it onto the roof after the shooting was over and it may have been open during the shooting.
Summing Up
There has been no mention of any other security personnel on the second floor. It is likely that the Butler County Sniper, with a clear view to Trump, was completely alone and unobserved. We now also know that his window was fully open.
Questions are being asked.