The news that Paul Manafort has been charged with a dozen serious offences in Robert Mueller’s Russian inquiry was not entirely unexpected, although it is a very significant development in the case being built against Donald Trump. What came as quite a surprise was the revelation that George Papadopoulos has pleaded guilty to the charges facing him.

George who? Even dedicated Trump watchers may ask. But Papadopoulos, who was part of the Trump foreign policy team, has information which fills in some crucial blanks and provides links to others being scrutinised by special counsel Robert Mueller as he seeks to establish whether Trump really was the “Muscovite Candidate” in the election.

The other reason why Papadopoulos, a Greek American who had once lived in London, is important is because he is evidently providing information to the investigators – a “proactive cooperator” as they put it. He is not, however, the only one doing this. Rinat Akmetshin, a Russian-American lobbyist who was present at a meeting between a Russian lawyer; Donald Trump Jr; President Trump’s son-in-law Jared Kushner; and Paul Manafort, has also now appeared before a grand jury.

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And then there is Felix Sater, a key to Trump’s alleged Russian money train. A criminal with connections to Russian and American organised crime, a man who has already been a federal informant in the past is now once again helping the authorities. Sater is believed to be providing information about a money laundering operation based in the former Soviet Republic of Kazakhstan which involved Trump properties.

So it is the fear of disclosure by the men with the secrets which will worry Trump and some people around him. It is hardly a secret that Mueller’s team would like “turn” Manafort, who faces a lengthy prison sentence and a massive fine if he is convicted of the various charges of money laundering, secret lobbying for a foreign power, lying to government investigators and sundry other matters.

Trump’s allies are already expressing their trepidation about this. Roger Stone, who helped launch the President’s election campaign and remains a close confidante, and is also former business partner of Manafort, complained last night: “Now I understand how this works, you try to find something Paul Manafort did 15 years ago and you call it money laundering, tax evasion, wire fraud – some nonsense. Then you say ‘Ok Manafort, we’re sending you to jail for 15 years unless you just admit that you were colluding with the Russians and Donald Trump knew everything.”

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We already know some of the things that Trump was aware of and, in the ensuing weeks and months, we shall find out more. Among the things both Papadopoulos and Manafort knew was that the Kremlin claimed to have dirt on Hillary Clinton. Papadopoulos had been told this by an academic in London and a Russian woman who, he thought, was Vladimir Putin’s niece. Papadopoulos had sent emails to the Trump election team about this while urging meetings with the Russians.

Manafort, Trump Jr and Kushner met the Russian lawyer Natalia Veselnitskaya in June 2016 at the Trump Tower hotel in New York because, it is claimed, she was offering to impart information Moscow supposedly had on Clinton. President Trump is then said to have personally dictated a statement in his son’s name saying the meeting “primarily discussed a programme about the adoption of Russian children” (adoption of Russian children by Americans was banned by Moscow in response to the Magnitsky Act in 2012). That statement by the President has become a key factor into whether he and those around him attempted to obstruct the investigation into Russian meddling in the US election.

Rinat Akhmetshin gave evidence under oath before a grand jury convened by Mueller for several hours on 11th June this year about, among other things, the Trump Tower meeting where he was taken by Veselnitskaya. Akhmetshin, a lobbyist, has acknowledged serving as a counter-intelligence officer in the Soviet military in the past. He is now, he said in a newspaper interview, “a mercenary”, but not a Russian spy and does not work for the Kremlin. “I spend other peoples’ money to achieve other peoples’ goals” was the way he explained his work. The Senate Judiciary Committee is investigating Akhmetshin’s US citizenship, his military background and whether he improperly lobbied for Russian interests.

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And then we come to Felix Sater who is likely to be centre-stage if Trump’s downfall comes from his Russian monetary connections. Born Felix Sheferovsky in Russia he is one of the most colourful characters in the Trump chronicles: someone once jailed for stabbing a man in the face with a cocktail glass (for a margarita) and who later avoided a possible 20-year sentence and $5m (£3.8m) fine by becoming a federal informer in another case, that of fraud and extortion by the mafia targeting the elderly, some of them Holocaust survivors.

In a recently unsealed transcript of a hearing in New York, the Justice Department described the value of Sater’s snitching. He had supplied information, it said, on Russian organised crime; American mafia families and al-Qaeda. Sater does not deny working for the government, but he says he did not inform on the mafia.

Sater became managing director of the Bayrock Group, a real estate firm which had offices two floors beneath the Trump Organisation’s headquarters in Trump Tower for eight years. Bayrock went into partnership with Trump in connection with the construction of the Trump SoHo hotel. The two men appeared at ribbon cutting ceremonies for joint projects and went on business trips, including one to Moscow, together. Sater used Trump Organisation business cards, though the Trump Organisation maintains he was not an employee.

Sater boasted that he was so close to the Trump family that he was asked by Donald to squire Donald Jr and Ivanka on a trip to Moscow and that during it he arranged for Ivanka to sit in Putin’s chair in the President’s office in the Kremlin. Ivanka acknowledges the trip took place and it may have involved sitting at Putin’s desk.

Sater is a lifelong friend of Michael Cohen, Trump’s lawyer and a former vice-president of the Trump Organisation. Sater was convinced that Putin would help Trump to get to the White House and he and Cohen would receive the credit due for this. “Can you believe two guys from Brooklyn are going to elect a president?” was the email sent to Cohen at one stage. He had stated, in earlier messages, that Putin would back the development of a Trump Tower hotel in Moscow and that this would be part of a grand plan. “Our boy can become President of the USA and we can engineer it … I will get Putin on this programme and we will get Trump elected.”

Cohen was named in the Trump report by former MI6 officer Christopher Steele as a key conduit between with the Russians through Putin’s spokesman Dmitri Peskov who was allegedly tasked with carrying out a covert campaign to undermine Hilary Clinton’s presidential bid (which Peskov denied). Cohen had initially denied having “any dealings” whatsoever with the Russians in his work for Trump. But newly leaked emails show that he asked for Peskov’s help with a Trump real estate project in Moscow in 2016 when Trump was already campaigning to secure the Republican nomination for the presidency, thus raising issues of conflicts of interest.

Andrew Weissmann, the prosecutor who “turned” Sater after the mafia extortion case and signed his plea bargaining deal is now in the Mueller team, one of many experienced lawyers who had left highly-paid jobs or taken leave of absence, to join the investigation.

Sater has agreed to help a federal inquiry into alleged money laundering by Viktor Khrapunov, Kazakhstan’s former energy minister and the former mayor of the city of Almaty who was charged by Kazakh authorities with abuse of power. He is on the Interpol wanted list at the behest of Kazakh authorities. Khrapunov’s family allegedly used shell companies to buy Trump SoHo properties worth an estimated $3.1m. It is not known if any or how much of the supposedly laundered money went to Trump.