The only one who loose with this death is the government.
A public hearing of Nisman at the Congress was going to be a big triumph for the government because prosecutors have inmunity unless they are caught in fraganti, Nisman was going to leave the Congress handcuffed (to disclosure a criminal investigation is a crime plus illegal phone tapping -over 300 cds- too).
There is a war going on inside the intellegence agency (they had their own agenda and they were working against the government: traitors) Nisman bought rotten fish and he finished dead.
The President released the secret on the secret agents who were involved on the illegal phone tapping because they were who used Nisman and, perhaps, who killed him if he was killed.