Well, if he didn't have these people killed without trials, then he should be found not guilty.
But he did have people killed without trials. Chile may have had a marxist president, but he was an ELECTED president, the independent courts were functioning and the people were free to critize the president (which they were doing) which was not the case with Pinochet. It seems to me we're supposedly fighting a war right now to bring democracy to a former dictatorship... and we want that dictator on trial. Why shouldn't the Chileans want their dictator to face his accusers?