BUENOS AIRES — Confronted with a deepening scandal, the president of Argentina shifted position on Thursday, saying that the death of the lead prosecutor investigating the 1994 bombing of a Jewish center was not a suicide as she and other government officials had suggested.

Instead, President Cristina Fernández de Kirchner suggested that the prosecutor’s death was part of what she hinted was a sinister plot to defame and destroy her.

The president’s change of position added a major new twist to the suspicious death of the prosecutor, Alberto Nisman, whose body was found in his luxury apartment in Buenos Aires late Sunday with a fatal gunshot wound to the head.

“As the days go by, instead of knowing more, we know less,” Carlos Pagni, a political commentator, wrote in a column in the newspaper La Nación, in which he pointed to the case’s “tide of unknown quantities.”