The theory and practice of secret information gathering. Academic Journal of Internal Affairs, [S. l.], v. 63, n. 9, p. 5–29, 2015. DOI: 10.38146/BSZ.2015.9.1. Disponível em: http://belugyiszemlejournal.pitservice.hu/index.php/belugyiszemle/article/view/196. Acesso em: 2 mar. 2026.