But the trove of documents, made public this week following a yearslong legal effort by media organizations, shed no new light on the part of the Russian-born businessman's past that is probably of the most interest to House Democrats investigating the president.
They don't get into his work with Trump on real estate projects in New York City and elsewhere in the years before he ran for president, and don't deal with the time period when Sater was pushing for a deal to build a Trump Tower project in Moscow.
U.S. District Judge Leo Glasser, who ordered the records released, ruled that some documents should remain secret, but assured the public that those materials contain "not a jot or tittle that mentions the President in relation to Sater."
A Soviet emigre who befriended Trump in the 2000s, Sater served jail time for slashing a man with a broken cocktail glass in 1991 and then was convicted of racketeering in 1998 for his role in a $40 million pump-and-dump stock fraud.
That conviction, though, was kept under seal for years as Sater provided intelligence to the FBI on a who's who of criminal organizations. Meanwhile, he reinvented himself as a real estate developer, working with a company that partnered with Trump on a hotel condominium project in Manhattan's SoHo neighborhood and repeatedly trying to work out a deal for a Trump branded property in Russia.
Sater's name appears dozens of times in Special Counsel Robert Mueller's report on Russian interference. He had multiple exchanges with Trump's former personal lawyer, Michael Cohen, as he pushed a Moscow project during the 2016 presidential campaign.
The skyscraper deal was later abandoned, and Cohen was sentenced to three years in federal prison after pleading guilty to tax evasion, campaign-finance violations and lying to Congress about the project.
In all the years he worked with the FBI, Sater said the authorities never asked him to provide information about Trump before Mueller inquired about the Moscow deal. He said additional court records that Glasser ordered to be unsealed next month will provide even more details about his globe-trotting efforts to combat terrorism.
"I love this country more than anything else," Sater told The Associated Press, adding he was not moved to cooperate by the possibility of a jail sentence. "I'm not trying to wrap myself in a flag, but I did this out of patriotism."
Sater was interviewed this month by U.S. House Intelligence Committee staff as part of the panel's inquiry into contacts between Russia and the Trump campaign. A spokesman for the committee's chairman accused Sater of not fully cooperating, saying Sater would remain under subpoena.
Sater told The AP he was forthcoming and "answered every question." Some details of Sater's exploits as a government source surfaced over the years in media accounts and through his own testimony, but the court documents unsealed this week offer the perspective of prosecutors and an FBI agent who put Sater in a league of his own among government cooperators.
Among the records unsealed at the behest of The Intercept, an online news organization, is a transcript of Sater's 2009 sentencing, in which prosecutors raved about his decade of cooperation. One FBI agent described Sater as the difference between failure and success in the bureau's then-nascent efforts to curb organized crime on Wall Street in the mid- to late-1990s.
Before Sater turned state's evidence, said Todd Kaminsky, then assistant U.S. attorney, "criminal financial wizards were one step ahead of law enforcement." The FBI, Kaminsky said, "would take any given investigation they were looking into at the time, bring it in front of Felix Sater, and he would explain to them what was going on."
"There was nothing he wouldn't do," he said. "No task was too big." Kaminsky credited Sater with implicating several high-ranking members in La Cosa Nostra, telling a federal appeals court in a later hearing that his cooperation "runs a gamut that is seldom seen."
"It involves violent organizations such as Al Qaida," he said, according to another newly unsealed transcript. "It involves foreign governments. It involves Russian organized crime." Sater's attorneys wrote in another court filing that he had given the government specific information about key leaders in Al Qaida and even traveled to the Middle East at the FBI's direction following the Sept. 11 terrorist attacks.
Sater wore a wire for so long during a decade of "constant undercover work" that it "got to a point where it became too dangerous to allow a confirmation of his cooperation to be known," Kaminsky said.
In the end, Sater was sentenced to probation and a $25,000 fine in the stock fraud case because of his work for the government. Federal prosecutors had argued for several years that records related to Sater's criminal case should be sealed because his life could be in danger if his cooperation was known, but Sater himself undermined that argument by giving interviews where he talked about his history as a cooperator on mob and terrorism cases.
Sater said he's hopeful any risk to his safety will fade as time goes by. "I made a decision to risk my life and do the things I did," he said. "There's nothing I can do about it now."