All the hijackers had assigned seats in first class, and they seem to have used them.
( ( ( ( ( ( All ( the hijackers ) ) ( had ( assigned ( seats ( in ( first class ) ) ) ) ) ) , ) and ) ( they ( seem ( to ( have ( used them ) ) ) ) ) ) . )
(ROOT (S (S (NP (PDT All) (DT the) (NNS hijackers)) (VP (VBD had) (VP (VBN assigned) (NP (NP (NNS seats)) (PP (IN in) (NP (JJ first) (NN class))))))) (, ,) (CC and) (S (NP (PRP they)) (VP (VBP seem) (S (VP (TO to) (VP (VB have) (VP (VBN used) (NP (PRP them)))))))) (. .)))
The hijackers sat in their assigned seats in first class.
( ( The hijackers ) ( ( ( sat ( in ( their ( assigned seats ) ) ) ) ( in ( first class ) ) ) . ) )
(ROOT (S (NP (DT The) (NNS hijackers)) (VP (VBD sat) (PP (IN in) (NP (PRP$ their) (JJ assigned) (NNS seats))) (PP (IN in) (NP (JJ first) (NN class)))) (. .)))