During the recent terrorist attack in Russia, the terrorists operated in the building for about 18 min. How could they set it on fire in such short time so that it burned to ashes and the roof collapsed?
The footage from outside shows very energetic fire and parts of the building flying away. According to reports, the fire was with efforts "localized" in the area of 4000 square meters.
From my experience, it could be problematic to set on fire a pile of wood in such short time.
So, how this could be possible if the terrorsts at most had backpacks with them?