Complex sentence: During the military government of 1976-1983, Brinzoni had been Secretary-General of the military government of Chaco Province and was accused of involvement in the'massacre of Margarita Belén' of 22 political prisoners on 13 December 1976.
Split into simpler sentences: During the military government of 1976--1983, Brinzoni was Secretary-General of the military government of Chaco Province. After the return to democracy, he was accused of involvement in the "Massacre of Margarita Belén", in which 22 political prisoners were executed on 13 December 1976.