@hightor,
Exactly. The undeniable presence of those planes makes any additional conspiracy logically impossible.
Let's call the conspiracy to torch the buildings with planes Plan A.
Plan B is the conspiracy to bring down the buildings with thermites.
Why oh why implement both plan A and plan B? They are redundant, as your brexiter says.
Therefore, there is no plan B. There's only one conspiracy's here: Plan A was implemented and led to the buildings' collapse.