The top court said today that US citizen Michael Townley, Chilean Armando Fernandez Larios and Cuban Virgilio Paz are co-authors in the killing of Carmelo Soria.
The 54-year-old Spanish diplomat was working for the UN's Economic Commission for Latin America.
The accused worked for the feared DINA secret police under Gen. Augusto Pinochet's 1973-1990 dictatorship.
Prosecutors say they apparently targeted Soria because they were convinced he had been helping Communists in Chile.