BPT emission line diagnostic diagrams. The K03 line in grey separates the SF galaxies and composite object regions, while the Ke01 demarcation line in black distinguishes between optically-classified AGN and composite objects. Left panel: NELG sample which consists of 797 sources (45% of BPT-AGN (green symbols), 31% composite objects (blue symbols) and 24% in the SF region (red symbols)). Right panel: NELG sample with high hard X-ray luminosity (L_HX> 10⁴² ergs^-1). There are 172 sources (54% of the sample) classified as BPT-AGN (green symbols), 103 sources (blue symbols) classified as composite objects and 41 sources (13%) in the SF region of the diagram (red symbols; our elusive AGN).