so the first alarm sounds as if it might have been a smoke alarm.
someone non technical was in charge to check. he/she looked up but he was 200 feet away and maybe there was something going on on top of a scaffold or ledge not visible from below.
he/she went back to their office without climbing up.
the smoke turned to fire.
maybe this is why arson is not suspected by authorities?
So, we should know more about who checked the first time, what they found, and how they carefully they checked and where they checked in relation to in relation to where the fire broke out.