(S (S (BASENP (NNS Observers)) (VP (VBP have) (VP (VP (VBN expressed) (BASENP (NN concern))) (PP (IN at) (NP (BASENP (DT the) (NN fact)) (SBAR (IN that) (S (BASENP (DT the) (NN bomber)) (VP (VBD was) (ADJP (JJ able) (S (VP (TO to) (VP (ADVP (RB successfully)) (VP (VB attack) (NP (NP (PDT such) (NP (DT a) (NP (ADJP (JJ high-profile) (CC and) (ADJP (RB heavily) (JJ guarded))) (NN target)))) (PP (IN as) (NP (NP (BASENP (DT the) (NN headquarters)) (PRN (COMMA ,) (PP (ADVP (RB especially)) (PP (VBG considering) (NP (BASENP (DT the) (NN building) (POS 's)) (NP (BASENP (JJ close) (NN proximity)) (PP (TO to) (BASENP (DT the) (NNP Tarbela) (NNP Dam) (NN generator))))))) (COMMA ,))) (VP (VBN considered) (BASENP (DT an) (JJ important) (JJ strategic) (NN asset))))))))))))))))))) (PERIOD .))