THAT THE mysterious death of an Argentine prosecutor has rattled President Cristina Fernández de Kirchner is all too evident from the president’s own postings on her Facebook page. Last Tuesday, Ms. Kirchner claimed in a rambling, 2,000-word post that Alberto Nisman, who was found dead of a gunshot wound to the head the night before he was due to publicly charge Ms. Kirchner with illicit dealings with Iran, had killed himself. On Thursday, she maintained in an even longer Facebook post that Mr. Nisman had been murdered as part of an elaborate plot against her government.

In fact, Mr. Nisman appears to have compiled considerable evidence that Ms. Kirchner and several other top officials attempted to strike a deal between 2011 and 2013 under which Iran would supply Argentina with oil in exchange for food, and Ms. Kirchner’s government would seek the removal from an Interpol arrest list of eight Iranians wanted in connection with the 1994 bombing of a Jewish community center in Buenos Aires. Both the charges and the prosecutor’s death call out for an independent, internationally-backed investigation.

The stakes of the case extend well beyond Argentina. Mr. Nisman has alleged that senior Iranian officials were involved in planning or approving the community center bombing. According to Andres Oppenheimer of the Miami Herald, Mr. Nisman said he had testimony that now-president Hassan Rouhani was one of the members of a committee that signed off on the attack. He told Mr. Oppenheimer, as well as a reporter for the Wall Street Journal, that he was looking forward to testifying to the Argentine Congress last Monday about a 280-page report he had delivered to a judge outlining the secret dealings between the two governments. No suicide note was found in his apartment following his sudden death last Sunday.

The evidence Mr. Nisman compiled included transcripts of phone conversations between Argentine and Iranian representatives. The sanctions-busting deal they were trying to arrange, the prosecutor charged, broke down when Argentine Foreign Minister Héctor Timerman was unable to persuade Interpol to remove the Iranians from its arrest list.

Ms. Kirchner’s claim that this case was fabricated by rogue intelligence officials is undermined by the fact that her government subsequently announced an accord with Iran under which the 1994 bombing would be investigated by a joint commission — which would have neutered the judicial process. This travesty did not go forward only because the Argentine Supreme Court declared it illegal.

Ms. Kirchner, whose populist, quasi-autocratic rule has badly damaged Argentina’s economy and soured its relations with the United States and other democracies, is a political lame duck who is due to leave office following an election later this year. However, she, Mr. Timerman and other close associates should be held accountable for their dealings with Iran. The cause of Mr. Nisman’s death must also be established. Only a probe with international sponsorship or participation is likely to produce a credible result. If Ms. Kirchner really believes herself to be the innocent target of a conspiracy, she should welcome it.