The explosive news that ousted national security advisor Michael Flynn pleaded guilty to lying to the FBI about his contacts with Russian officials was delivered in a brief, tidy package: a one-and-a-half-page document laying out the single count against him.

Former federal prosecutors told TPM that Special Counsel Robert Mueller made a calculated move to keep Flynn’s charge limited, and that, given what is known about Flynn’s myriad inappropriate foreign dealings, they wouldn’t have done so unless the former intelligence official had divulged some very juicy secrets.

“What’s interesting to me is what he’s not charged with,” said Steven Miller, a former anti-corruption federal prosecutor. “This is a very narrowly drawn structural plea bargain. By virtue of a single count he can’t get more than a five-year sentence. You don’t get that unless you’re giving something serious to the government. And the number of players left are relatively small: it’s [Jared] Kushner, it’s [Donald] Trump Jr., it’s the Trump campaign, and it’s the President. So I think this is something that would cause all of them to be extraordinarily worried.”

“It’s a neon sign that there’s massive cooperation underway by Flynn,” Miller added.

Jens Ohlin, an expert in criminal law at Cornell Law School, concurred, saying what essentially amounts to a “sweetheart deal” would not be offered unless Flynn could incriminate a bigger fish.

“The government would not agree to this deal if Flynn was merely providing information on someone who is in a peripheral place in the criminality,” Ohlin said. “So if he’s providing information in exchange to this deal its because it’s someone who is even more centrally located than Flynn.”

Shortly after Flynn entered a guilty plea in Washington, D.C. federal court, the White House released a statement downplaying the news. White House attorney Ty Cobb’s claim that “nothing about the guilty plea or the charge implicates anyone other than Mr. Flynn” was rapidly proven false by the release of Flynn’s statement of offense.

That document affirmed that “a very senior member” and “senior official” of the Trump transition team told Flynn to contact Russian and other foreign government officials to discuss critical foreign policy decisions.

Former prosecutors say that Flynn must have entered into a proffer, or “queen for a day,” agreement with Mueller’s team in which he divulged every detail he knew relevant to their investigation. The government found the information sufficiently valuable that they agreed to strike a deal, despite Flynn’s undisclosed lobbying on behalf of Turkey and reported discussions about spiriting an exiled Muslim cleric loathed by Turkey’s government out of the U.S.

The decision not to include a violation of the Foreign Agents Registration Act for his Turkey lobbying or other possible charges in Flynn’s plea agreement is not as unusual as it may seem.

“They have discretion to do whatever they want,” Seetha Ramachandran, a former Justice Department official and assistant U.S. attorney said of federal prosecutors. “The practice really varies between different federal districts. Some U.S. attorneys offices and parts of [Main] Justice want a cooperator to plead guilty to everything they’ve ever done. Some use a more bare-bones type of guilty plea. So I think it really varies. He’s chosen this strategy.”

Mueller’s camp has carefully managed the release of information about other Trump officials who may be caught up in the probe, but details on Flynn’s work to lobby on behalf of Israel with Kushner are already emerging in the press. Much more will come out in the days to come, legal experts predicted.

“I think this is the tip of the iceberg,” said Steve Vladeck, a national security expert at the University of Texas School of Law.

“The question is whether we’re going to start hearing stuff from Flynn’s camp about what he’s sharing with investigators, whether we’re going to see more movement, more indictments coming down in the next couple of weeks from Mueller. The real story of today is that there’s a guarantee that there’s big news coming down the pike.”