The state news agency Telman says lower court Judge Fabiana Palmaghini made the decision Tuesday. The move effectively pushes the case to federal court.
Palmaghini's decision comes a day after she heard testimony by South American nation's most famous spymaster, Antonio Stiuso, about his relationship with Nisman.
Stiuso had assisted Nisman's investigation of the unsolved 1994 bombing of a Buenos Aires Jewish center.
Nisman was found shot dead in his apartment on Jan. 18, 2015. Days before his death, Nisman accused then-President Cristina Fernandez of helping Iranian officials cover up Iran's alleged role in the bombing that killed 85 people. The case against Fernandez was later thrown out.
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