 According to the local outlet Beaver Countian, which broke the story, quote, a security operations plan had placed each of the three counter snipers inside of the building looking out of windows toward the rally with none stationed on its roof. Due to a lack of manpower, the men did not have spotters assigned to them as would be standard operating procedure. So maybe the excuse is that they couldn't spare anyone to watch the roof. They just ran out of people.