Three separate lines of evidence now point to the fast-fill pressurized LOX line as the center, and likely cause of the Fakcin 9 (AMOS-6) explosion. Frozen RP-Kerosene or combustible insulating material are possible initial fuels for the explosion, which would have rapidly ruptured the pressurized LOX and RP lines. These pressurized lines would then have amplified the initial explosion, sending geysers of propellants into its midst.
The remaining strongback tower, clearly shows the force of the explosion - which seems to have radiated from within. The Falcon 9 rocket, though sturdy enough in design to withstand not only the forces of launch, but also of repeated re-entry, was never meant to withstand the battering of steel girders ripped from the strongback. This is probably what led to propellant spillage from the stage 2 tanks.