The death of a prosecutor who had accused Argentina's president of a criminal conspiracy came under mounting questions Wednesday with the discovery that the apartment where he was found dead had not been securely locked and had a third entrance.

The locksmith who opened the back door to give investigators access to the home where Alberto Nisman was found dead said that it was barely closed, raising questions about whether a killer might have entered what was earlier described as a securely locked 13th-story apartment.

After testifying to investigators, the man who gave his name only as Walter said he was able to quickly open the door with a hook. He added, "If someone entered or not, I don't know."

And the official news agency Telam said investigators had found a third access to the home, a narrow passage holding air conditioning equipment that connects to a neighboring apartment. They were investigating a seemingly recent footprint found inside.

Initial official reports of the scene had strongly suggested a possible suicide: a securely locked apartment and no evidence of another person involved.

But widespread suspicion that Nisman was killed, as well as the release of his 289-page report detailing allegations against President Cristina Fernandez, caused a crisis for the government, which scrambled to promise "maximum transparency and cooperation" in the investigation into the death of a man accusing the president of a criminal conspiracy to cover up "crimes against humanity."

The Ipsos polling company said 70 percent of 414 people it questioned soon after news of the death believed it was murder.

Nisman, 51, was found slumped in the bathroom of his apartment Sunday night with a bullet wound in his head and a .22 caliber handgun beside his body.

He died four days after formally asking a judge to open a criminal case against the president and her foreign minister and a day before he was to detail those allegations to congress.

Lead prosecutor Viviana Fein said there was no evidence of anyone else involved in the death, but said Nisman left no suicide note. A test of his hand showed no residue of gunpowder, though she said that may have been due to the small caliber of the gun. The fact that national Security Secretary Sergio Berni quickly turned up in the apartment also fed doubts.

Fein said the gun found beside Nisman was registered to another man, Diego Lagomarsino, described by officials as a colleague of Nisman, who reportedly gave it to him on Saturday.

Nisman had spent 10 years investigating the 1994 bombing of a Jewish community center in Buenos Aires that killed 85 people, the worst terror attack in Argentine history.

His full report, released late Tuesday, accused Fernandez and Foreign Minister Hector Timerman of reaching agreement with Iran to avoid prosecution of several Iranians charged with involvement in the bombing. He said that would open a lucrative trade in Argentine grains and meat for Iranian oil.

In the end Interpol never dropped its "red notices" for the arrest of five of the Iranians, however, and the government said trade with Iran has diminished.

Writing with passion, Nisman called it "a criminal plan to erase at a stroke the serious accusations that weigh on the Iranian fugitives ... something unprecedented and never before seen."

The document did not appear to show direct or documentary evidence of a deal, but it did include wiretap transcripts of several people discussing such negotiations and saying the deal was approved by "la jefa" — Spanish for a female "chief" — and "at the highest level."

Among those involved in the talks, Nisman said, was a key suspect in the bombing, Mohsen Rabbani, former cultural attache at the Iranian Embassy in Buenos Aires.

The government dismissed Nisman's allegations as "weak" and "baseless" and Fernandez on Tuesday released a long message saying Nisman's investigation was meant "to divert, to lie, to cover up and confuse" ahead of a trial of former President Carlos Menem and other officials for a separate alleged cover-up of the bombing.

Nisman was appointed to his post in 2005 by then-President Nestor Kirchner, Fernandez's husband, after a bungled 10-year probe launched under Menem that led to a trial in which all the defendants were found innocent.

Nisman won arrest orders against several Iranians, including several current and former officials, and Interpol later put five of them on its most-wanted list.

But the case made little progress and, in 2013, Argentina and Iran agreed to jointly investigate the attack. Nisman alleged that was a cover for a secret pact that would actually protect the Iranian suspects.