Castillo started working in 1980 as a photojournalist in Palermo for daily newspaper L'Ora and the agency Informazione fotografica by Letizia Battaglia and Franco Zecchin. In 1987, Castillo collaborated for "Action Press" in Hamburg on issues in Eastern European nations such as Romania, Poland, Hungary, and Yugoslavia. In 1986 and also from 1994 to 1996, he realized monographic dossiers for Iberian television TV3.
In 1994 in Rome, he worked for the national newspapers and magazines Il Corriere della Sera, la Repubblica, Il Messaggero, La Stampa, L'Unità, Avvenire, Panorama, L'Espresso, Famiglia Cristiana, and Diario, along with the international magazines and newspapers The Boston Globe, The Guardian, The Washington Post, International Herald Tribune, El País, La Vanguardia, El Tiempo, El Mundo, The Australian, and Der Spiegel.
From 1995 to April 2002, he worked for Agenzia Nazionale Stampa Associata (a.k.a. ANSA), an Italian news Agency in Rome. From June 2002 to January 2004, worked for the Associated Press in Rome. He has been working for ANSA since December 2005.