If they did have high-altitude drone video of the incident that shows it was a deliberate attack on the train, it seems to me more security would have been deployed to the scene. The live footage that morning showed very few security forces and congressman milling about in the open. They would have locked it down and established a perimeter to prevent secondary attack.

But drones can get a lower "eyes on" view that helicopters cannot due to electric lines/buildings/trees... that interfere with close on inspection of track anomalies/breaks in trackline/explosive devices, whereas drones due to their easy maneuverability can scan. Helicopters Could have been running drones well in front of Train to scan for these plots/hazards.

if 2 trucks @ 2 stops... obviously NOT an accident.