At the same time or shortly thereafter, Atta-the only terrorist on board trained to fly a jet-would have moved to the cockpit from his business-class seat, possibly accompanied by Omari.
( ( At ( ( the ( same time ) ) ( or ( shortly thereafter ) ) ) ) ( , ( ( ( Atta-the ( only terrorist ) ) ( on ( board ( trained ( to ( fly ( a jet-would ) ) ) ) ) ) ) ( ( have ( ( moved ( to ( the cockpit ) ) ) ( from ( ( ( his ( business-class seat ) ) , ) ( possibly ( accompanied ( by Omari ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN At) (UCP (NP (DT the) (JJ same) (NN time)) (CC or) (ADVP (RB shortly)) (ADVP (RB thereafter)))) (, ,) (NP (NP (JJ Atta-the) (JJ only) (NN terrorist)) (PP (IN on) (NP (NP (NN board)) (VP (VBN trained) (S (VP (TO to) (VP (VB fly) (NP (DT a) (NN jet-would))))))))) (VP (VBP have) (VP (VBN moved) (PP (TO to) (NP (DT the) (NN cockpit))) (PP (IN from) (NP (NP (PRP$ his) (ADJP (JJ business-class)) (NN seat)) (, ,) (VP (ADVP (RB possibly)) (VBN accompanied) (PP (IN by) (NP (NNP Omari)))))))) (. .)))
Atta and Omari were two terrorists who were armed with box cutters.
( ( ( Atta and ) Omari ) ( ( were ( ( two terrorists ) ( who ( were ( armed ( with ( box cutters ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Atta) (CC and) (NNP Omari)) (VP (VBD were) (NP (NP (CD two) (NNS terrorists)) (SBAR (WHNP (WP who)) (S (VP (VBD were) (VP (VBN armed) (PP (IN with) (NP (NN box) (NNS cutters))))))))) (. .)))