He has published numerous books and zines, including El cerdo volador, Pánico, Juventud moderna, and Ciudades convertidas en selvas with publishers in Peru and other South American countries. In 2003, Cossio was awarded a Rockfeller Foundation Fellowship in the Humanities along with two other authors (Luis Rossell and Alfredo Villar).  Thanks in part to this grant, his group was able to produce the graphic novel Rupay—Historias gráficas sobre la violencia política 1980–1984.  His most important work to date is Barbarie—Cómics sobre la violencia política 1985–1990, a collection of graphic stories that denounce the atrocities committed by the Peruvian armed forces and the Maoist group Shining Path (Sendero Luminoso) during the years of internal conflict in this Andean nation (1980–2000).  He has been an invited panelist at important Latin American comic book festivals including Viñetas con altura 2009 (Bolivia), Viñetas sueltas 2009 and 2010 (Argentina) and Entreviñetas 2012 (Colombia).  He is considered by critics as one of the most influential authors of documentary and journalistic comic books in Latin America.