On the morning of September 11, 1973, Chileans awoke to news that their country's three military branches were in the process of waging a joint-coup d'état that would lead to the ousting of the world's first democratically elected socialist president, Salvador Allende.

That day, Chile's military surrounded and bombed the presidential building in Santiago with many top officials inside — including Allende, who delivered a sign-off speech before shooting himself just as the military stormed into the building. Subsequent days and weeks saw thousands of leftists rounded up, detained, and killed. Nearly two decades of an Augusto Pinochet-led dictatorship followed, with well-documented instances of torture and disappearances.

Criminal proceedings — and much debate — surrounding the Pinochet regime in the South American country remain ongoing. But the pursuit of justice has implications that reach all the way to Washington DC, and a group of activists and archivists in the US continue to push the US government to declassify documents related to America's clandestine involvement in the coup and its aftermath.

Employees are seen exiting La Moneda on September 11, 1973 upon surrendering to General Augusto Pinochet. Photo via AP.

Thousands of documents have been released in the last 15 years as a result of these efforts and a separate special project launched under the Clinton administration. But some of the key details have yet to be declassified and important questions are still unanswered — largely pertaining to the murky historical ruling over the extent to which the US was actually involved.

"There are still documents out there," Peter Kornbluh, the director of the Chile Project at the National Security Archives, told VICE News. Specifically, he discussed some of the major documents that remain classified, some concerning US operations against Allende prior to the coup, cooperation with Pinochet's government, details of the murder of two Americans, and a Chilean secret police head who was on the CIA's payroll.

Kornbluh and the National Security Archives — along with activists and organizations — were behind the campaign to persuade the Clinton administration to begin declassifying the documents. Further propelled by Pinochet's arrest in London in 1998, the State Department established the Chile Declassification Project the following year with an initial release of nearly 6,000 documents from the State Department, CIA, National Archives, FBI, and the Department of Defense.

"Chile is one of those iconic cases of immorality and atrocity," Kornbluh said. "The world will not rest until all the documents are released ... and all the criminals alive in Chile are held accountable."

The years between Allende's historic presidential win in 1970 and his subsequent overthrow are filled with an array of events that make for a complicated history. Allende did not receive a majority vote, and the subsequent nationalization of the copper mining industry, as well as proposed land reforms, did not help him win over critics. The country was ripe with discontent, and Allende was also lacking a fan base in the US government.

Files released through the declassification project have provided a window into then-US Secretary of State Henry Kissinger's distaste for Allende. Kissinger's candid phone transcripts, released in 2013, show he played a key role in developing the administration's US-Chile policy. Specifically, Kissinger directly relayed to Nixon that Allende needed to be ousted because his "'model effect can be insidious."

According to the phone transcripts, just days after Allende's win, Kissinger told a CIA chief, "we will not let Chile go down the drain." Three days later, during a brief meeting with the intelligence agency, President Nixon gave orders for the CIA to "make the economy scream."

Kornbluh said that Kissinger and other officials continue to misrepresent the role the US played, especially in regard to the military, an issue Kornbluh said has not received enough attention because the public has been "waylaid by issues of the CIA role in Chile."

"There is no better way to engage than newly declassified documents to reiterate Kissinger and Nixon's [actions]," he said.

"It's important for a verdict of history, which people like Henry Kissinger try to misrepresent," Kornbluh explained, discussing why the continued declassification is important. For the likes of Kissinger, he said, "We'll never have a courtroom verdict, but at least we'll have a historical verdict for which documents of that are critically important."

While these documents have given a window into the US government's involvement in Chile during the 1970s, the search for details continues. Mauricio Paredes, director of Syracuse University's program in Chile, told VICE News that questions still remain regarding the role US agents might have played in training Pinochet's notorious secret police (the Dirección de Inteligencia Nacional, or DINA) on Chilean territory.

"For now, there is [only] a testimony of a former Chilean agent," he explained. "However, they are missing official documents."

Kornbluh also brought up another case related to the CIA and DINA for which details remain classified. In one of the first rounds of documents released in 2000, information confirmed that the former head of the secret police, General Manuel Contreras, was at one point on the US intelligence agency's payroll. In addition to reigning over the dictatorship's many detention centers, known for torturous acts that were routinely carried out, Contreras also played a role in coordinating the assassination of a Chilean diplomat on US soil.

According to Kornbluh, Contreras was eventually taken off the CIA's payroll, but the documents related to this decision are still sealed. He said access to these details is fundamental due to the general's alleged role in torture, not to mention for understanding the CIA's thought process.

"Someone stepped in and took him off the payroll," Kornbluh said. "You could imagine the internal debate going on."

The official presidential building, La Moneda, in Santiago after it was bombed by fighter jets during the 1973 military overthrow of Salvador Allende and his government. Photo via AP.

Four decades later, it's easy to neglect the importance of US involvement in the military coup and dictatorship in Chile, but Kornbluh and Paredes stress the need to continue pushing for more.

At the most basic level, Paredes said the documents are needed "to fill the historical gap" — referring to the fact that Pinochet's regime destroyed its archives prior to being democratically ousted from power through a popular vote plebiscite in 1988. It took until 1990 for the country to formally transition to democracy. Paredes explained that this could be especially important because many Chileans "deny the human rights violations and dictatorial policies of Pinochet."

According to Kornbluh, unclassified documents are also important for a courtroom verdict against members of the Chilean military and civilians who collaborated with the dictatorship. Many crimes and atrocities have not been prosecuted or remain unclear, some of which include the murders of Americans during the regime, as Paredes pointed out.

Paredes said the details surrounding the murders of American journalists Charles Horman and Frank Teruggi, as well as the disappearance of Penn State professor Boris Weisfeiler have not been clarified. In a high profile case that saw a development this summer, a Chilean court ruled that US military intel served a key role in Teruggi and Horman's deaths in the days following the coup.

While documents related to this case — which was turned into the Hollywood movie Missing in 1982 — have been released, Kornbluh said actual evidence of what happened is lacking, even in the files that were used by the Chilean court.

Despite the remaining questions, Kornbluh said Chile is a unique case — "unlike any country" — in terms of the US government providing documents. So far, some 23,000 documents have been released to the public, a striking figure compared to other scandals.

"Should all the documents be declassified? They absolutely should be," Kornbluh said. "Are they still being declassified? Yes they are."

Pooja Jhunjhunwala, a US state department spokesperson, said Chile has "created a strong and thriving democracy," and the two governments are working together to "promote our shared values, including respect for human rights and the promotion of open government practices."

As for the records, Jhunjhunwala said, "The United States has declassified and released to the public extensive documentation related to events in Chile before, during, and after the events of September 11, 1973. These documents allow anyone to review the nature and extent of US policies and actions during that period." She noted that many of the declassified documents are available on the Department of State's FOIA website.

According to Kornbluh, a batch of files was released this spring, and another is set for the fall. There are dumps planned for the coming year as well, specifically those related to the 1973-1976 post-coup period.

While presidential administrations may have stressed the importance of declassifying documents, Kornbluh said the CIA hasn't always aligned with these goals.

"The secrecy system is a very forcible system and the declassification system is very bureaucratic," he said, noting that there should be a special classified project for many US-related scandals. "Every anniversary and every article is a catalyst to press for more openness and hidden records."