With former US national security advisor Mike Flynn’s guilty plea for lying to the FBI, special prosecutor Robert Mueller now has serious leverage on three of president Donald Trump’s top 2016 campaign officials in his probe of Russian meddling in the presidential election.

In October, former campaign chairman Paul Manafort and his top aide Rick Gates were hit with 12 charges including “conspiracy against the United States.” Manafort has spent a month contemplating his thoughts under house arrest, agreeing yesterday (Nov. 30) to a $12-million bail deal with Mueller’s team. Now Flynn faces up to five years in jail and a $250,000 fine, with Mueller also probing his alleged role in a Turkish government plot to kidnap the dissident cleric Fethullah Gülen from the US.

Manafort, Flynn and Gates might have the most information about exactly what went on during Trump’s campaign. They all also have documented ties to Russia—Manafort and Gates spent years working for pro-Russian former Ukrainian president Viktor Yanukovych, while Flynn has made speaking visits to Moscow and taken money from state TV channel RT.

Cooperation from a low-level campaign official, foreign policy advisor George Papadopoulos, revealed a fascinating trove of information, including his attempts to set up a meeting between Trump and Russian president Vladimir Putin and the fact that the campaign knew of claims that the Russians had Democratic candidate Hillary Clinton’s emails as early as April 2016. There’s been speculation that Papadopoulos wore a wire to get hold of incriminating evidence since then.

Still, anything Papadopoulos may deliver likely would be tiny in comparison to someone like Flynn, one of Trump’s earliest supporters and most trusted advisors, whom the president called a “very good man” even after effectively firing him in February for misleading vice president Mike Pence.

As University of New Hampshire law professor Seth Abramson writes, the way flipping a prosecutorial target normally works—getting someone to offer incriminating information on another person higher up in the organization—would imply that bigger names are in Mueller’s sights. What’s more, if Flynn is only being prosecuted for lying to the FBI about his Russia contacts despite the questions about his Turkish connections, that could suggest whatever he’s offering is very big indeed. Anything he can give prosecutors may put Gates and Manafort under more pressure to offer up nuggets of their own.