Every rulling house have have it own 'secret police' for luck of better word. As I understand EB2 is based on Kingdoms so I guess there is ability to establish such kind of organization to development tree of every faction except for nomads like Saka (I don't know if they follow such rules). Tbh I belive it is a must for every hellenic influenced kingdom and SPQR. Agents and assassins should be recruted only via such 'police' not markets like merchants.