BUENOS AIRES — The president did it. No, it was the Argentine spymaster plotting against her. Maybe it really was a suicide, the tragic fall of a man whose case was coming undone. Or was it Iran, the Israeli Mossad, the C.I.A.? And what about the lingering influence of the Nazis who fled here after World War II?

Ever since the fatal shooting of Alberto Nisman, the prosecutor who accused President Cristina Fernández de Kirchner of conspiring with Iran to cover up responsibility for the bombing of a Jewish community center, this country has been awash in theories about who pulled the trigger, and why.

Whether in hushed conversations in cafes, at corner news stalls, or at a lonely beach town hot-dog stand, much of Argentina seems to have an idea about how Mr. Nisman ended up on his apartment floor with a gunshot wound to the head — the night before he was scheduled to testify about his accusations to lawmakers.

“It has to either be the armed faction of narco-Nazi-jihadist international terrorism, or it has to be the Jewish-Marxism mafia that also involves the C.I.A., Israel and the Mossad,” said Carlos Wiesemann, 65, a hot-dog vendor in the town of Pinamar, weighing his list of suspected forces while drinking whiskey with a friend.