Alberto Nisman, who investigated Argentina’s worst terrorist attack before he was found dead in his home last year, may have been forced to kill himself, a prosecutor who was formerly in charge of his case has said.

Viviana Fein, who in December was removed from the investigation into Nisman’s mysterious death, had said before that it was likely suicide.

But in an interview with local radio station La Red, she acknowledged for the first time that it was possible he was “induced” to kill himself.

Fein said that Nisman had several back-and-forth calls with “six or seven people”, including the country’s former spy chief, Antonio Stiuso, and then-army chief Cesar Milani on 18 January 2015. The body of Nisman, who led the probe of the 1994 AMIA Jewish center bombing in Buenos Aires that killed 85 people, was discovered on that day in his apartment with a gunshot wound to the head.

“I find it suggestive and noteworthy that personalities of this calibre were on the same day of his death talking uninterruptedly,” Fein said.

Nisman had been scheduled to appear in Congress the next day to present allegations that then president, Cristina Fernandez, orchestrated a secret deal to cover up the alleged role of Iranian officials in the attack. Fernandez denied the allegations and judges threw out the case.

Nearly 18 months after Nisman’s death, authorities have yet to determine whether he took his own life or was killed by someone else.

Conspiracy theories have flourished around the case. While some people including his family believe Nisman killed himself because he felt his claims against the former president lacked proof, others say he was murdered because he was a threat to the Argentine and Iranian governments.