HILLARY'S SERVER PROBE
Peter Strzok was a key investigator into Hillary Clinton's handling of classified intelligence when she was Secretary of State. Here is how his role affected the key players.
Huma Abedin: Cleared despite telling untruths
Hillary Clinton's right-hand woman was interviewed by Strzok and questioned about her knowledge of the existence of Clinton's secret server.
Strzok wrote a summary of the interview which said: 'Abedin did not know that Clinton had a private server until about a year and a half ago when it became public knowledge.'
In fact, Abedin had been involved in a series of email exchanges which demonstrated that she knew about the server, including one from an IT aide which said: 'I had to shut down the server. Someone was trying to hack us...'
Cheryl Mills: Cleared despite telling untruths
Mills was chief of staff and counselor to Clinton when she was Secretary of State.
Strzok summarized the interview with her which he conducted in April 2016, saying: 'Mills did not learn Clinton was using a private server until after Clinton’s tenure. Mills stated she was not even sure she knew what a server was at the time.'
In fact, a series of emails from the time demonstrated that neither assertion by Mills could be true.
'HRC email coming back — is server okay?' Mills emailed to Justin Cooper, the IT aide in February 2010.
Despite that email, Strzok accepted that she did not know what a 'server' was at the time.
In August 2011 she received an email from Stephen Mull, a State Department IT official, which said Clinton had asked for a new Blackberry which was malfunctioning 'possibly because of her personal email server is down'.
Abedin was also sent the email.
Hillary Clinton: Cleared her of criminal level gross negligence by removing term from critical Comey memo
Then FBI Director James Comey sent a message to three top officials in the bureau on May 2, 2016, summarizing the latest position on the Clinton probe.
It included the damning sentence: 'There is evidence to support a conclusion that Secretary Clinton, and others, used the private email server in a manner that was grossly negligent with respect to the handling of classified material.'
The phrase 'grossly negligent' was critical as that is the standard which needs to be reached to bring a federal prosecution for mishandling classified intelligence. In other words, Comey was saying that she should be charged.
But the language was changed on June 10 and the phrase 'grossly negligent' replaced by Strozk with 'extremely careless' - below the standard for prosecution.
The memo then formed the basis for James Comey's July statement on Clinton which said she would not be charged.
THE RUSSIA PROBE
After Robert Mueller was appointed Special Counsel to look into allegations of collusion between the Trump campaign and Russia, Strzok was assigned to his team. He was removed when his anti-Trump texts to his mistress came to light. Here is what is known and what is still unknown about his actions
Mike Flynn: Oversaw interviews where he lied to FBI
Strzok was the official overseeing FBI interviews of Mike Flynn, the former general who was Trump's first national security adviser.
It is unknown exactly how many times Flynn was interviewed by the FBI but he dramatically pleaded guilty last Friday to lying to the feds in an interview in January when he was still in office.
Flynn admitted lying about his dealings with Sergey Kislyak, then Russia's ambassador to the U.S.
He was interviewed at least once more and now faces a sentence of up to five years in prison for his crime.
However, it appears likely he will receive a far lighter sentence as he is a cooperating witness with the Mueller investigation and has even agreed to take part in covert evidence-gathering for the FBI.
Jared Kushner and other Trump officials: Did he oversee interviews and charges?
Mugshot: George Papadopolous, first Trump aide to plead guilty in the Mueller probe
As the FBI's most senior counter-intelligence agent on the Mueller taskforce, it appears certain that Strzok would also have overseen the interviews it is known the FBI has conducted so far, but his involvement has not been confirmed.
One of those questioned by FBI agents includes Jared Kushner, the president's son-in-law.
Others known or reported to have been interviewed include Hope Hicks, now Trump's White House director of communications.
She had been his campaign spokeswoman and steamed his suits while he wore them on his plane.
Paul Manafort, Trump's former campaign director, was interviewed by the FBI after his home was raided in a dramatic pre-dawn entry, and has now been charged with counts including conspiracy.
Also charged was Rick Gates, Manafort's aide in the campaign and Manafort's long-time right-hand man.
And the first guilty plea in the Mueller probe was by George Papadopolous, a campaign aide who admitted lying to the FBI. Again Strzok's role is still to be made public.