For years, Felix Sater — an associate of President Donald Trump’s who played a key role in the investigation into Russian election interference — told people that he was building “Trump Towers by day and hunting bin Laden by night” on covert missions around the world on behalf of the US government. The stories were so wild that many dismissed them as obvious fiction.

But a secret government document, released today by a federal judge, confirms that Sater acted for years as a covert asset of the US government and provided intelligence that “included, but was not limited to, (a) Osama bin Laden’s whereabouts following September 11, 2001; (b) the internal structuring and the financial capabilities of al-Qaeda; (c) the whereabouts of Taliban leader Mullah Omar; (d) ground reports on who was killed by United States air-strikes; (e) the details of an assassination plot against President Bush; and (f) information on North Korea’s nuclear capabilities.”

Much of the government’s account about Sater’s remarkable double life was previously reported by BuzzFeed News in 2018.

The partially redacted government document, referred to as a 5K1 letter in legal parlance, said that Sater went undercover and was instrumental in weakening the Mafia’s presence on Wall Street. He also “played a crucial role” in helping the US government dismantle money laundering operations in Russia, Cyprus, Turkey, and elsewhere. And, the letter continued, “Sater also provided information about the identities of organized crime leaders in Russia and the roles they occupied in the organized crime hierarchy. He provided information about the American business interests of Russian oligarchs and the ties these individuals had to organized crime figures.”

Federal prosecutors wrote the 10-page letter in 2009 to help Sater get a lenient sentence after his conviction in a 1998 racketeering case. The letter was released on Friday afternoon by US District Court Judge I. Leo Glasser in response to a lawsuit by the Intercept.

“For approximately ten years, Sater continuously worked with prosecutors and law enforcement agents to provide information crucial to the conviction of over twenty different individuals, including those responsible for committing massive financial fraud, members of La Cosa Nostra organized crime families and international cyber-criminals,” wrote Benton J. Campbell, the US attorney for the Eastern District of New York. The letter was signed by Todd Kaminsky, an assistant US attorney in the office who is now a New York state senator. “Additionally, Sater provided the United States intelligence community with highly sensitive information in an effort to help the government combat terrorists and rogue states.”

His cooperation “was of a depth and breadth rarely seen,” Campbell wrote.

In an interview with BuzzFeed News, Sater said he is happy the government revealed the extent of his cooperation.

“Given the events of the last three years, I'm happy that people can now judge me for the bad that I've done and the good that I've done,” he said. “I just hope that 20 years of service to protect America adds a little to the plus column.”

The letter also details Sater’s crimes. It describes how, in his mid-twenties, Sater and three associates swindled investors out of $40 million and then “carefully laundered” it through offshore accounts with the help of organized crime figures.

In September 1998, eight months after the New York Police Department discovered documents in a storage locker that detailed the stock fraud as well as his role in it, Sater, who had been overseas, surrendered to the FBI. By that time, the letter said, he was already unofficially working for the US government and collecting intelligence from sources in Afghanistan.

“In an effort to build a reserve of good will for the imminent prosecution he was to face in America, Sater contacted United States intelligence officers overseas and offered to provide them with information concerning Afghanistan’s Northern Alliance,” the letter said. “During the spring and summer of 1998, Sater traveled to Central Asia where he gathered and passed on information to United States sources about the Northern Alliance’s desire to resell Stinger missiles to the United States government as well as information about the Taliban and Osama bin Laden, among other things. Sater contacted the FBI during this period and kept agents apprised of his activities overseas.”

Sater pleaded guilty to racketeering charges in 1998 and entered into a cooperation agreement with the US government that was signed by Andrew Weissmann, then an assistant US attorney, who nearly two decades later would become a key member of special counsel Robert Mueller’s prosecution team.

In addition to the letter, Glasser also unsealed a redacted version of a 13-page sentencing memorandum Sater’s then–defense attorney, Leslie Caldwell, filed with the court arguing for leniency. It contains even more details about Sater’s work for the US government. She wrote that Sater provided the FBI with information on bin Laden's location after the 9/11 attacks as well as “a list of Al Qaeda members, names and locations of people who handled security for Bin Laden, secret meetings that Bin Laden planned to attend, a list of Sudanese banks where Bin Laden held cash reserves, and the identity of companies that were controlled by Bin Laden in various parts of the world.”

Throughout her career, Caldwell at points worked with Weissmann, the prosecutor who approved Sater's cooperation deal, when both worked for the Department of Justice. Caldwell was also once appointed to a job at the US attorney’s office in California by Robert Mueller when he was the US attorney for the Northern District of California. Sater hired her in the mid-2000s when she was working in private practice.

The FBI declined to comment about Sater's work for the bureau. The CIA did not respond to a request for comment.

Sater emerged in 2017 as a high-profile figure in Mueller’s Trump–Russia investigation after emails between him and Trump’s former personal attorney, Michael Cohen, showing a years-long effort to build a Trump Tower in Moscow and to “get Donald elected” in the process were leaked and became public.

BuzzFeed News previously obtained documents that showed the negotiations between Sater and Cohen to try to break ground on a Trump Tower project in Moscow continued through at least June 2016, by which time Trump was already the Republican frontrunner, contradicting Cohen’s sworn congressional testimony that the discussions ended in January 2016, weeks before the start of the Iowa caucuses.

Sater was interviewed multiple times by Mueller’s team and a grand jury, and he testified three times before House and Senate intelligence committee investigators about the Trump Tower Moscow plans. He is mentioned by name more than 100 times in Mueller’s final report on Russian interference in the 2016 election and President Trump's campaign.

After he was identified as a central figure in the Trump–Russia probe, reporters dug into Sater’s past. Many media outlets reported in general terms on the work he had done for the US government on high-stakes national security and terrorism cases, but his account was often treated with a measure of skepticism.

The government makes clear that Sater was not exaggerating about his extensive cooperation with US agencies, which began before his involvement in real estate development with the Trump Organization and continued, according to Sater and law enforcement sources, until at least late 2017.

The US attorneys said Sater worked with several high-ranking Russian military and former KGB officers to gather intelligence about Afghanistan and the Middle East and threats to the US. One of these military officers, BuzzFeed News reported last year, was also involved in Sater and Cohen’s efforts to build a Trump Tower in Moscow.

The letter said Sater provided “specific, detailed information to the Central Intelligence Agency (‘CIA’), FBI and other agencies” in 1998, which included “what were believed to be bin Laden’s satellite telephone numbers and information about who was supplying arms to bin Laden.”

The letter said people in the intelligence community “with knowledge of the information Sater provided” told the US government it “was taken very seriously and was carefully analyzed.” However, some intelligence officials have publicly questioned the value of the information Sater provided. But a half dozen current and former intelligence sources who are familiar with Sater’s case and worked on the al-Qaeda threat before and after 9/11 told BuzzFeed News much of the intelligence he provided was “actionable.” One intelligence source said the information Sater shared about the terrorist organization was “very useful” to “ongoing US operations” in Afghanistan immediately after 9/11.

Sater continued to gather intelligence on al-Qaeda and bin Laden after the 9/11 attacks, working with a precious stones dealer who had his own intelligence contacts inside the Taliban and Northern Alliance. The FBI purchased a satellite phone that Sater shipped to this person "so the two could remain in constant contact."

“Sater went above and beyond what is expected of most cooperators and placed himself in great jeopardy in so doing,” the letter said. “Throughout the near ten-year period that Sater cooperated with the government, he worked continuously with a number of agents who supervised his activities. Without exception, every one of these agents has told the government that Sater was an exemplary cooperator who worked diligently to further the aims of the missions to which he was assigned.”

At his sentencing in 2009, Judge Glasser told Sater: “For 11 years, I would suspect you had gone to bed every night or every other night sleeping a little restlessly and wondering what your sentence is going to be. So, in effect, there has been a sentence which already has been imposed.”

Sater did not serve any jail time. For the $40 million stock scheme, he was fined $25,000.