Argentina suspects rogue agents from its own intelligence services were behind the death of a state prosecutor investigating the deadly 1994 bombing of a Jewish community center in Buenos Aires.
Alberto Nisman was found dead in his apartment late on Sunday, a gunshot wound to his head and a 22 caliber pistol by his side along with a single shell casing.
He had been scheduled to appear before Congress on Monday to answer questions about his allegation that President Cristina Fernandez conspired to derail his investigation of the attack.
His death and a blizzard of conspiracy theories around it have rocked Argentina.
Investigators have said Nisman appeared to have committed suicide, but have not ruled out homicide or an "induced suicide."
The government says Nisman's allegations and his death were linked to a power struggle at Argentina's intelligence agency and agents who had recently been fired.
It says they deliberately misled Nisman and may have had a hand in writing parts of his 350-page complaint.
"When he was alive they needed him to present the charges against the president. Then, undoubtedly, it was useful to have him dead," the president's chief of staff, Anibal Fernandez, said on Friday.
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Argentine courts have accused a group of Iranians of planting the 1994 bomb, which killed 85 people.
Nisman claimed last week that President Fernandez opened a secret back channel to Iran to cover up Tehran's alleged involvement in the bombing and gain access to Iranian oil needed to help close Argentina's $7 billion per year energy deficit.
Fernandez's government called the accusation absurd.
Iran has repeatedly denied any link to the bomb attack.
The Argentine government's chief of staff said on Friday that he didn't believe Nisman even wrote his own report.
"I have worked quite a bit with prosecutor Nisman. I know he was a well qualified expert in the law. He could not have written this nonsense," he said. "It is totally clear he had nothing to do with it, but there were people around him who had a different agenda."
Although the government says there was a conspiracy to falsely accuse the president and then do away with Nisman, no one has been arrested in the case so far.
Also on Friday, justice officials said they have been unable to locate the man who loaned Nisman the gun used in his death despite "repeated attempts," and were ordering that he be barred from leaving the country without first getting permission from Argentine authorities. The man gave the gun to Nisman the day before his death, saying he had given a .22-caliber pistol to Nisman because the prosecutor wanted it for protection.
Diego Lagomarsino had turned himself in for questioning after the news broke but has not been taken into custody. Lagomarsino has not been named as a suspect.
Officials initially said Nisman's death looked like suicide, but the lead investigator says it is suspicious and that all leads are being followed.
Meanwhile, Argentine police was investigating the 10 police officers assigned to protect Nisman for their actions on the day the prosecutor was found shot to death.
The officers, along with two supervisors, are being looked at as part of an internal police investigation into the handling of Alberto Nisman's death, a person close to the investigation told The Associated Press on Friday on condition of anonymity.
The officers are not considered suspects, said the person, who was not authorized to comment publicly.
In particular, he said, investigators are looking into the time it took two officers assigned to the door of Nisman's building to advise their superiors that they had not been able to reach him by telephone.
Earlier this week, those two officers made declarations to lead investigator Viviana Fein, who would ultimately decide whether to try them for anything. All 10 have been suspended during the investigation, the person close to the case said.
The head of Argentine intelligence was replaced in December, resulting in the firing of agents who had been helping with Nisman's investigation. Nisman had accused agents from another faction within the state intelligence apparatus of being part of Fernandez's alleged plot to clear the Iranian suspects.
One of those fired in the December shakeup was Antonio Stiusso, a senior spy who had helped Nisman with the probe.
The government says Stiusso falsely told Nisman that two men implicated in the case against the president were state intelligence agents. Wire tapped phone conversations of the two were key to Nisman's accusation that the government was trying to whitewash the 1994 car bombing.
President Fernandez said on Thursday that she did not believe Nisman took his own life.
"Nisman's accusation never was, in itself, the true operation against the government ... The true operation against the government was his death, after accusing the government," she said in a post on Facebook.
Those close to the late prosecutor have doubted from the beginning that he killed himself. Friends described him as upbeat ahead of his scheduled appearance before Congress on Monday.
The Associated Press contributed to this report.