The revelation probably means Nisman intended to file arrest warrants after spelling out his findings to Argentina's lawmakers, said Mark Dubowitz, a friend of Nisman's and executive director of the Foundation for Defense of Democracies, a Washington think tank.
Nisman in 2006 had accused members of Iran and its Lebanese Shiite ally, Hezbollah, in the 1994 bombing that killed 85 people in Buenos Aires. He had issued eight arrest warrants. In 2013, Kirchner signed a memorandum of understanding with Iran to jointly investigate the case. That agreement was declared unconstitutional by an Argentine court last year.
Nisman had accused Kirchner of reaching the deal to shield Iran from prosecution in return for access to Iranian oil. Fein is investigating whether Nisman committed suicide or was murdered.
Damian Pachter, the reporter who first wrote of Nisman's death, flew to Israel fearing he was being followed and would be killed next, according to an interview with the Israeli newspaper Haaretz.
The arrest warrants were not part of an 289-page criminal complaint against Kirchner, Timerman and their supporters that Nisman had filed, according to The New York Times.
In her defense, Kirchner said that Nisman was overly influenced by her enemies among Argentina's intelligence services, and she called last week for the country's spy service to be disbanded.
Dubowitz, who worked with Nisman on Iran-related issues, said he has been "skeptical from the start" about the investigation into Nisman's death.
"How many prosecutors, after seeing what happened to Alberto, will be willing to literally put their lives on the line to take on Kirchner" and Argentina's security services, Dubowitz said.
Kirchner is trying to destroy Nisman's reputation, but he "can't defend himself from the grave," he said. "She's going to have to contend with a lot of documentary evidence that substantiates his original thesis."