A United States jury convicted President Donald Trump's former adviser Roger Stone on Friday, finding the longtime Republican operative and self-proclaimed "dirty trickster" guilty on seven criminal counts of lying to Congress, obstruction and witness tampering.

The verdict, in a trial arising from investigations of Russian interference in the 2016 US election, is not only a blow to Stone but renews scrutiny on then-candidate Trump's activities at a time when he faces an impeachment inquiry that could derail his presidency.

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The 67-year-old veteran Republican political operative - a self-described "agent provocateur" - was charged earlier this year with obstructing justice, witness tampering and lying to the US House of Representatives Intelligence Committee during its investigation into Russian interference in the 2016 presidential election.

Trump almost immediately reacted to the news, tweeting: "So they now convict Roger Stone of lying and want to jail him for many years to come. Well, what about Crooked Hillary, Comey, Strzok, Page, McCabe, Brennan, Clapper, Shifty Schiff, Ohr & Nellie, Steele & all of the others, including even Mueller himself?"

He added: "A double standard like never seen before in the history of our Country?"

Colourful trial

Stone's colourful trial in federal court in Washington, DC, was as much about the rough-and-tumble world of politics, as it was about hair-splitting legal arguments, such as whether Stone truly lied about WikiLeaks since that website was never explicitly mentioned in the intelligence committee's publicly-stated parameters of its investigation.

The trial featured testimony by political heavyweights including former Trump campaign CEO Steve Bannon and former Trump campaign deputy Rick Gates, each of whom said they believed Stone had inside information about when WikiLeaks might release more damaging emails about then-Republican candidate Trump's Democratic opponent Hillary Clinton.

Roger Stone, former adviser to President Donald Trump, and his wife Nydia Stone arrive at the court [Mark Wilson/Getty Images/AFP]

Prosecutors accused Stone of telling politicians five different lies related to WikiLeaks and its founder Julian Assange, which in 2016 dumped a series of damaging emails about Clinton that US intelligence officials and then-Special Counsel Robert Mueller later concluded had been stolen by Russian hackers.

Some of those lies relate to the existence of certain texts or emails, while others pertain to Stone's conversations with Trump campaign officials and a supposed "intermediary" with WikiLeaks in early August 2016 whom Stone identified to politicians as being comedian Randy Credico.

Prosecutors said Stone did not actually start talking to Credico about WikiLeaks until later that month, and the actual person to whom he was referring in testimony as an "intermediary" was conservative author Jerome Corsi whom Stone dispatched in an email to "Get to Assange!" and get the emails.

Corsi was not called as a witness in the trial.

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Stone, a close Trump ally who famously has the face of former president Richard Nixon tattooed on his back, was also accused of tampering with a witness, Credico, when Credico was summoned to testify before Congress and speak with the FBI.

Stone and Credico, who took the stand in the case, have since said that Credico did not act as a WikiLeaks backchannel.

In emails and texts, the jury saw messages that Stone had sent Credico that included comments like "Prepare to die", "You're a rat. A stoolie", and "Stonewall it. Plead the Fifth. Anything to save the plan", in a reference to a famous Nixon Watergate quote.

He also repeatedly urged Credico to "do a Frank Pentangeli" - a reference to a "Godfather II" character who recants his congressional testimony against a mobster amid intimidation.

A lawyer for Stone dismissed the Pentangeli reference, saying Credico had done impressions of the character in the past, and said the "odious language" they used was just part of how they interacted.

A federal judge scheduled Stone's sentenced for February 2020.