BUENOS AIRES — Argentina’s government on Wednesday cast greater suspicion on an aide to Alberto Nisman, the prosecutor whose mysterious death this month has shaken the country, by describing the aide as an intelligence operative — adding to its assertions that rogue spies were involved in the events around Nisman’s death. Lagomarsino worked in the prosecutor’s investigative unit as an information technology consultant and lent Nisman the .22-caliber Bersa pistol used in his death, investigators say. Before Nisman was found dead in his apartment this month, he made the explosive assertion that President Cristina Fernandez had tried to reach a secret deal with Iran to shield Iranian officials from responsibility in the 1994 bombing of a Jewish cultural center in Argentina, which killed 85 people. Investigators have not determined whether Nisman committed suicide or was killed, but Fernandez’s government has suggested that Nisman was being manipulated by an ousted spymaster at the country’s main intelligence agency, the Intelligence Secretariat.