Argentina's president says prosecutor Nisman's death may not be suicide

With its tangled series of rapidly-changing events, the murder mystery of Argentinian special prosecutor Alberto Nisman is turning into a growing political scandal.

Under mounting political pressure, President Cristina Fernandez, also known as Cristina Fernandez-Kirchner, has now admitted his death might not have been a suicide after all, reports CBS News Correspondent Michelle Miller.

Nisman was found dead in his Buenos Aires apartment on Sunday in what prosecutors said appeared to be a suicide. The day after, he had been set to deliver damning evidence in the case of a 1994 bombing of a Jewish center, implicating the country's president in a cover-up.

Thousands of Argentinians, many holding signs of solidarity saying "I am Nisman" took to the streets, demanding a full investigation into the death of the well-known prosecutor. He was found with a fatal gunshot wound to the head, but without any gunpowder residue on his hands.

Fernandez also originally dismissed his death as a suicide, but on Thursday, in a letter posted to her website, Kirchner implied he was murdered, killed by her opponents to smear her reputation.

"They used him alive," she wrote, "and then they needed him dead."

In a complete about-face, the president said on social media sites that the questions over Nisman's death "have been converted into certainty. The suicide (I'm convinced) was not a suicide."

"I think what the president finds herself in is an incredibly difficult political position," CBS News senior national security analyst Juan Zarate said. "Hard one to defend. And that explains her vacillating statements."

Nisman's death is testing Fernandez's credibility as opponents accuse her of a cover-up.

Nisman was the lead prosecutor in the case of a Jewish center car bombing in 1994, that left 85 dead. He long blamed Iran for the attack, but died the day before he was set to reveal critical evidence, much of which came from secret wire taps. It implicated Fernandez and her top aides in a secret deal to shield Iranian officials from prosecution allegedly in return for lucrative "grain for oil" trade deals.

The Argentinian government will now have to juggle three high-profile investigations: the 1993 bombing, the alleged political cover-up and now the death of Nisman.

"That's another unanswered question which is, who will take up the mantle for Alberto Nisman? In many ways he was a singular figure in Argentina in prosecuting these cases," Zarate said.

Polls show that 70 percent of Argentinians believe Nisman was murdered, and 82 percent said his allegations against government officials were credible.