Complex sentence: In 1954 he became co-director of La Prensa newspaper alongside his cousin and partner, Pedro Joaquín Chamorro Cardenal, who was assassinated by Somoza supporters in 1978.
Split into simpler sentences: In 1954 he became co-director of "La Prensa" newspaper alongside his cousin and partner, Pedro Joaquín Chamorro Cardenal. Chamorro was assassinated by Somoza supporters in 1978.