(S (S (SBAR (WHNP (WP What)) (S (VP (VBD happened) (PP (IN at) (BASENP (DT the) (NN border)))))) (VP (VBD was) (NP (BASENP (DT the) (JJ sole) (NN responsibility)) (PP (IN of) (NP (BASENP (DT the) (JJ Rwandese) (NNS officials)) (VP (VBN involved))))))) (PERIOD .))