Comment: One very obvious reason why

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In reply to comment: If it really was planned, (see in situ)

One very obvious reason why

is because if they only used explosives and no planes involved, then an ensuing investigation would have taken place as to "HOW" did the explosives get placed and access to the building etc.

A whole bunch of questions would have begun to which how could they answer?

Nobody could ever wire those buildings without help from security and others and that would have led to some names and the truth coming out as to who and why.

My 2 cents

Peace

" In Thee O Lord do I put my trust " ~ Psalm 31:1~