That determination, likely to be made public in the coming days, contradicts the findings of another team of experts during Mrs. Kirchner’s tenure that there was no evidence anyone else was involved in Mr. Nisman’s death, meaning that hehad probably killed himself.
The saga of the prosecutor has long consumed Argentina, for good reason. He had been in charge of investigating the still-unsolved 1994 bombing of a Jewish community center in Buenos Aires that killed 85 people. Before his death, he accused Mrs. Kirchner and members of her government of trying to shield Iranian officials suspected of playing a role in the attack as part of a deal that would supply Iranian oil to Argentina.
Supporters of President Mauricio Macri, whose minority coalition in Congress is expected to pick up seats in the election on Oct. 22, say the latest report validates their longtime contention that Mr. Nisman was a victim of foul play.
By contrast, allies of Mrs. Kirchner, who has denied any wrongdoing, characterized the new forensic report as an effort by the current government to further undermine her image. Ms. Kirchner faces charges in several corruption investigations.
Credit Victor R. Caivano/Associated Press
But in the run-up to the election, Mrs. Kirchner has a mystery of her own to point to: The disappearance of Santiago Maldonado, an indigenous rights activist who, supporters say, vanished after border guards took him into custody.
The disappearance has outraged many Argentines, and Mrs. Kirchner contends that the government is simply putting forward the new allegations about Mr. Nisman’s death in order to distract attention from the case now unfolding on its watch.
“This is an immense smoke bomb to hide Santiago Maldonado,” Mrs. Kirchner said in a radio interview. Mr. Maldonado’s family and human rights groups have called for a protest on Sunday to mark the two-month anniversary of his disappearance.
The latest forensic investigation into Mr. Nisman’s death was carried out by a team of 28 experts. Over the course of nine months, they reconstructed the scene where his body was found in his bathroom, with a single gunshot wound to the head. They concluded the prosecutor was killed by two people, according to the senior judicial official, who has seen the report.
The forensic experts discovered several injuries on Mr. Nisman’s body — including a nasal fracture, a hematoma in his kidney, lesions on his legs and a wound on the palm of his hand — that they say are consistent with an attack on the prosecutor before he was killed. According to the official, investigators also said they found ketamine, an anesthetic, in Mr. Nisman’s blood, which they suspect was used to sedate the prosecutor before he was shot. No gunpowder residue was found on his hands, which they said made the suicide theory implausible.
Two teams of forensic experts, including a prestigious unit that operates under the purview of the Supreme Court, had previously said that there was no evidence that anyone else was in Mr. Nisman’s bathroom when he died.
Mr. Nisman’s former wife, Federal Judge Sandra Arroyo Salgado, has long said that she believes he was murdered. Mrs. Kirchner at first suggested Mr. Nisman had committed suicide, but she later backtracked, saying she was convinced he was killed to tarnish her government.
Julio Raffo, an opposition lawmaker who is not allied with Mrs. Kirchner, said in an interview that a group of experienced foreign forensic experts should be empaneled to examine all the reports and make a ruling that is not politically suspect.
“This is very alarming; everything related to this case is strange,” said Mr. Raffo, who has long been convinced Mr. Nisman was murdered, and has called on a judge to investigate whether previous forensic examiners covered up evidence.
Diego Lagomarsino, a computer technician who worked with Mr. Nisman, is so far the only person charged in the case, for giving the prosecutor the gun with which he was shot. A team of forensic experts and lawyers representing Mr. Lagomarsino have challenged the murder theory, arguing that suicide remains the most likely scenario.
Credit Marcos Brindicci/Reuters
The prosecutor in charge of the case, Eduardo Taiano, must now review all the evidence to decide whether to recommend labeling Mr. Nisman’s death a murder rather than a “suspicious death.”
The government is urging caution.
“We have to be super prudent with this,” the head of the president’s cabinet, Marcos Peña, told reporters in late September. “We have to wait for the courts to rule.”
While allies of Mr. Macri are focusing on the latest developments involving Mr. Nisman, supporters of Mrs. Kirchner have turned the apparent disappearance of Mr. Maldonado, 28, into a rallying cry.
The case has reverberated across much of the country, reviving memories of the mass disappearances and killings that took place during the brutal 1976-1983 dictatorship.
Tens of thousands of people took part in a demonstration over the disappearance on Sept. 1, which ended in violent clashes between demonstrators and the police.
Human rights activists have criticized Mr. Macri´s administration for quickly coming to the defense of the border guards who evicted the indigenous rights protesters in Patagonia. Mr. Maldonado had taken part in the protest. Government officials insist that the search for him continues.
“I just don’t know what to believe anymore,” said Ana Patricia Baliño, a 38-year-old accountant in Buenos Aires. “Everyone seems to be lying.”
Many share her skepticism. A recent poll by Management & Fit, a consultancy, found that three out of every four Argentines said they had little or no confidence in the country’s judiciary.
Around 40 percent of Argentines believe that Mr. Maldonado will never be found, according to a poll by Giacobbe & Asociados in early September. Shortly after Mr. Nisman’s death, 59 percent of Argentines said the truth of what happened to him would never be known.
“The general public is disgusted by the way in which politicians fight among each other to win points with complicated cases, rather than focusing on figuring out what happened,” said Jorge Giacobbe, a public opinion analyst.