(S (S (BASENP (NNS Gunmen)) (VP (VBD had) (VP (VP (VP (VP (VBN kept) (PRT (RP up))) (BASENP (DT a) (JJ 24-hour) (JJ hostage-taking) (NN assault))) (BASENP (JJ last) (NN month))) (PP (IN at) (BASENP (DT those) (JJ same) (NNS headquarters)))))) (PERIOD .))