Five years ago this week, on Dec. 9, 2014, the Senate completed the largest investigative review in its history: "The Committee Study of the Central Intelligence Agency's Detention and Interrogation Program." The review, commonly known as the Senate Torture Report, details a CIA program to secretly detain and torture suspected terrorists after the attacks of Sept. 11, 2001. It is a dark chapter in the nation's history — and one that remains open.

As the Senate staffer who led the investigation, I have welcomed seeing the facts of the CIA program reach a wider audience with the recent release of the film "The Report" and the audiobook of the Senate's executive summary, read by members of the film's cast. But there is still much for the American people to know. After all, the executive summary that was declassified and released publicly represents less than 8% of the full report.

The Senate investigation officially began in 2009, with a 14-to-1 bipartisan vote by the Intelligence Committee to expand an inquiry that had begun two years earlier into two CIA officers' destruction of videotapes depicting the CIA's treatment of two detainees.

For years, the CIA had assured the Senate that it did not engage in torture. However, through its inquiries, the Senate learned that the CIA used what it called "enhanced interrogation techniques," which included waterboarding, forced standing, extended sleep deprivation and confinement in small boxes, as well as other coercive treatment. These tactics have long been defined by the government as torture and a violation of U.S. and international laws. The Senate's "tapes investigation" lasted 14 months and included a review of classified documents, some of which described the interrogation of the CIA's first detainee, Abu Zubaydah.

The CIA had claimed that Zubaydah was uncooperative and that only after being subjected to the CIA's enhanced interrogation techniques did he provide critical, "otherwise unavailable" intelligence that had "saved lives" by disrupting specific terrorist plots. The documents reviewed by the Senate showed that these CIA representations were grossly inaccurate.

In fact, Zubaydah provided more, and better, intelligence during his first two months of detention than he did during the two months during and after the use of the CIA's torture tactics. These included being subjected to at least 83 waterboarding sessions. According to the classified records, the CIA ultimately declared that the interrogation was effective, not because it resulted in intelligence that disrupted plots but because the CIA was able to conclude that Zubaydah did not possess such information.

It was details such as these that led the Senate to expand its initial investigation to cover the CIA's entire Detention and Interrogation Program — and led to a CIA document-production phase that lasted more than three years. In total, 6.3 million pages of classified material were provided to the Senate, including operational cables, reports, memorandums and e-mails. This is equivalent to the materials found in two metropolitan libraries.

From these materials, the Senate uncovered additional misrepresentations and abuses and also found that the CIA itself had internally concluded that the torture was ineffective. The CIA later acknowledged that nearly a quarter of those it held as suspected terrorists should never have been detained.

After seven years of reviewing internal CIA records and documenting those records in a classified report, the Senate Intelligence Committee, in 2014, with a strong bipartisan vote of 11 to 3, agreed to send a 525-page executive summary to President Barack Obama for declassification. It then took nine months of negotiations among the committee, the White House and the CIA to come to agreement on alterations and redactions to the summary, as well as for the final, 6,779-page report, with 38,000 footnotes to CIA records, to become an official Senate record (albeit classified and unavailable to the public).

Still, five years after the release of the torture report's executive summary, and with many of the details about the CIA program still restricted from public view, former CIA leaders continue to defend the torture program as appropriate and effective. Their influence is felt in movies such as "Zero Dark Thirty," and at the International Spy Museum in Washington, where children can climb into a replica of the CIA's smallest confinement box and hear a former CIA official promote the torture program as "successful," one that "saved American lives." This is unacceptable and indicates that declassifying the full torture report is necessary.

I believe it is possible to do so. Each step in the Senate's investigation moved forward with bipartisan support. Indeed, one lesson of the torture report is that aggressive bipartisan oversight is possible. Congress should work swiftly to ensure that the American public knows the full details of what the CIA did in its name. And with these facts transparently laid out, and with a commitment to never commit these crimes again, we can close this dark chapter once and for all.

Daniel J. Jones was the lead investigator for the Senate Select Committee on Intelligence from 2007 to 2016. He wrote this article for the Washington Post.