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)))))) (. .)))
United Airlines contracted security screening work out to Argenbright Security.
( ( United Airlines ) ( ( contracted ( ( security screening ) ( ( work out ) ( to ( Argenbright Security ) ) ) ) ) . ) )
(ROOT (S (NP (NNP United) (NNPS Airlines)) (VP (VBD contracted) (S (NP (NN security) (NN screening)) (VP (VB work) (PRT (RP out)) (PP (TO to) (NP (NNP Argenbright) (NNP Security)))))) (. .)))