There's been some pretty interesting analysis based on the pattern of damage to the strongback frame and piping. Generally coming to the conclusion that Space-X had a nubie accident with LOX, in which insulation around the main oxygen charging pipe became saturated with oxygen (condensing from both the air and the oxgen venting.)
LOX and thermal insulation equals an explosive, that can even spontaneously ignite. It blew parts of the strongback apart, blasting the shrapnel through the rocket.
It's interesting Space-X hasn't said anything about that theory. Maybe because it's such a basic goof, they might risk insurance payouts or something like that?
I've been collecting links:
20161105
Spacex Explosion; Before and After - Seems to Reveal the Cause - Falcon 9 (AMOS-6) Loss
Early Shrapnel Tells a Story - Spacex Pad Anomaly Explosion Mechanism and the COPVs
Sep 28, 2016
Strongback Explosion Destroyed the Falcon Rocket - The Evidence (So Far) - AMOS-6
Spacex Exploding Strongback Shrapnel, and it's Destruction of the Falcon 9 Rocket
20161122
Exact Falcon Explosion Conditions - Illustrated by JCSAT Mission - Revealing Cause and Prevention