I'll freely admit my total ignorance of aircraft composites, but according to other posts, the vertical stabilizer was repaired during manufacture by attaching a doubler onto the base of the stabilizer, along with some rivets. I know that in the case of ordinary fiberglass, you have to be *very* careful with fitting anything where it isn't designed to be fitted, because you are putting a hole in something that depends on not having holes for a large portion of its strength. Also, rivets provide a channel for moisture ingress into the core of the structure, which can cause later delamination. Could the manufacturing repair be the root cause of this accident?
Sympathies to all those affected by this dreadful accident.