All five hijackers passed through the Main Terminal's west security screening checkpoint; United Airlines, which was the responsible air carrier, had contracted out the work to Argenbright Security.
( ( ( ( ( All ( five hijackers ) ) ( passed ( through ( ( the ( Main ( Terminal 's ) ) ) ( west ( security ( screening checkpoint ) ) ) ) ) ) ) ; ) ( ( ( ( ( United Airlines ) , ) ( which ( was ( the ( responsible ( air carrier ) ) ) ) ) ) , ) ( had ( ( ( contracted out ) ( the work ) ) ( to ( Argenbright Security ) ) ) ) ) ) . )
(ROOT (S (S (NP (DT All) (CD five) (NNS hijackers)) (VP (VBD passed) (PP (IN through) (NP (NP (DT the) (NNP Main) (NNP Terminal) (POS 's)) (JJ west) (NN security) (NN screening) (NN checkpoint))))) (: ;) (S (NP (NP (NNP United) (NNPS Airlines)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBD was) (NP (DT the) (ADJP (JJ responsible)) (NN air) (NN carrier))))) (, ,)) (VP (VBD had) (VP (VBN contracted) (PRT (RP out)) (NP (DT the) (NN work)) (PP (TO to) (NP (NNP Argenbright) (NNP Security)))))) (. .)))
None of the hijackers were able to pass the security screening checkpoint.
( ( None ( of ( the hijackers ) ) ) ( ( were ( able ( to ( pass ( the ( security ( screening checkpoint ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NN None)) (PP (IN of) (NP (DT the) (NNS hijackers)))) (VP (VBD were) (ADJP (JJ able) (S (VP (TO to) (VP (VB pass) (NP (DT the) (NN security) (NN screening) (NN checkpoint))))))) (. .)))