(S (S (BASENP (JJ Human-rights) (NNS groups)) (VP (VBP say) (SBAR (S (NP (QP (ADVP (IN at) (JJS least)) (NN 15)) (NNS people)) (VP (VBD were) (VP (VBN killed) (PP (IN by) (BASENP (NN security) (NNS forces))))))))) (PERIOD .))