Perhaps the terrorists stabbed the flight attendants to get a cockpit key, to force one of them to open the cockpit door, or to lure the captain or first officer out of the cockpit.
( Perhaps ( ( the terrorists ) ( ( ( stabbed ( the ( flight attendants ) ) ) ( ( ( ( ( ( to ( get ( a ( cockpit key ) ) ) ) , ) ( to ( ( force ( one ( of them ) ) ) ( to ( open ( the ( cockpit door ) ) ) ) ) ) ) , ) or ) ( to ( ( ( lure ( the ( captain ( or ( first officer ) ) ) ) ) out ) ( of ( the cockpit ) ) ) ) ) ) . ) ) )
(ROOT (S (ADVP (RB Perhaps)) (NP (DT the) (NNS terrorists)) (VP (VBD stabbed) (NP (DT the) (NN flight) (NNS attendants)) (S (VP (VP (TO to) (VP (VB get) (NP (DT a) (NN cockpit) (NN key)))) (, ,) (VP (TO to) (VP (VB force) (NP (NP (CD one)) (PP (IN of) (NP (PRP them)))) (S (VP (TO to) (VP (VB open) (NP (DT the) (NN cockpit) (NN door))))))) (, ,) (CC or) (VP (TO to) (VP (VB lure) (NP (DT the) (NN captain) (CC or) (JJ first) (NN officer)) (PRT (RP out)) (PP (IN of) (NP (DT the) (NN cockpit)))))))) (. .)))
It could be, that the terrorists stabbed the flight attendants to lure the captain or first officer out of the cockpit so they could stab them too.
( It ( ( could ( be ( , ( that ( ( the terrorists ) ( ( stabbed ( the ( flight attendants ) ) ) ( to ( ( ( ( lure ( the ( captain ( or ( first officer ) ) ) ) ) out ) ( of ( the cockpit ) ) ) ( so ( they ( could ( ( stab them ) too ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (MD could) (VP (VB be) (VP (, ,) (SBAR (IN that) (S (NP (DT the) (NNS terrorists)) (VP (VBD stabbed) (NP (DT the) (NN flight) (NNS attendants)) (S (VP (TO to) (VP (VB lure) (NP (DT the) (NN captain) (CC or) (JJ first) (NN officer)) (PRT (RP out)) (PP (IN of) (NP (DT the) (NN cockpit))) (SBAR (IN so) (S (NP (PRP they)) (VP (MD could) (VP (VB stab) (NP (PRP them)) (ADVP (RB too))))))))))))))) (. .)))