Donald Trump’s former lawyer told Congress on Wednesday that the president’s eldest son signed a check to fund illegal hush money payments to a pornographic actor, potentially placing Donald Trump Jr in legal peril.

Michael Cohen showed a House committee a check signed by Trump Jr reimbursing Cohen for payments to Stormy Daniels, who alleged she had an affair with Trump, according to a source familiar with Cohen’s plans.

Cohen, who spent a decade as Trump’s enforcer, also said Trump had advance knowledge of plans by WikiLeaks to release stolen Democratic emails and of a meeting his son held with Russians during the 2016 election campaign.

Play Video 3:32 Key moments from Michael Cohen's explosive testimony – video

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A copy of Cohen’s prepared remarks to the House oversight committee was obtained by the Guardian. He declared his former boss was a racist, a conman and a cheat.

“Today, I am here to tell the truth about Mr Trump,” Cohen said.

The finding that Donald Jr was directly involved in the scheme to pay off Daniels, whose real name is Stephanie Clifford, could mean the president’s son faces legal jeopardy. Federal prosecutors in New York, who have had copies of the checks and other records for months, say the payments violated campaign finance laws.

Cohen is the first Trump associate to publicly allege that the president had inside information about WikiLeaks releasing Democratic emails, which US intelligence agencies say were hacked by Russian operatives working to help Trump’s campaign.

Trump received the information on WikiLeaks in the days before the Democratic party convention July 2016 in a telephone call from Roger Stone, his longtime friend and adviser, according to Cohen, who said the call was placed on speakerphone.

“Mr Stone told Mr Trump that he had just gotten off the phone with Julian Assange and that Mr Assange told Mr Stone that, within a couple of days, there would be a massive dump of emails that would damage Hillary Clinton’s campaign. Mr Trump responded by stating to the effect of ‘wouldn’t that be great.’”

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Trump has denied knowing about the hacking of Democratic emails or of plans for their release. Stone previously claimed to have been in touch with Assange, the founder of WikiLeaks, but now says that he was lying about this.

Stone, whose public statements have been restricted by a judge’s gag order, said on Wednesday: “Mr Cohen’s statement is untrue.”

Robert Mueller, the special counsel, is concluding a two-year investigation into any links or coordination between Russia and the Trump campaign. Trump’s campaign chairman, Paul Manafort, is accused of sharing polling data with an alleged Russian intelligence operative. Trump has dismissed Mueller’s inquiry as a “witch hunt”.

Cohen also said that he recalled Donnald Trump Jr, the president’s eldest son, telling his father “in a low voice” in early June 2016: “The meeting is all set.” Cohen claims this was a reference to Donald Jr’s now-infamous gathering with several Russians, including a lawyer with ties to the Kremlin, at Trump Tower that month.

Play Video 2:09 Michael Cohen: Trump knew about Don Jr's meeting with Russians – video

“I remember Mr Trump saying, ‘OK good … let me know,” Cohen said in his prepared remarks. He said Trump had previously complained that Donald Jr “had the worst judgment of anyone in the world” and would not have set up a meeting of such significance without clearing it with his father.

Trump told Mueller in a series of written answers last year that he did not discuss WikiLeaks with Stone and did not know of the Trump Tower meeting in advance, according to CNN.

Profile Who is Michael Cohen? Show Hide Michael Cohen was a lawyer for Donald Trump from 2006 until 2018. He was a vice-president of The Trump Organization, and was part of Trump’s campaign team for the 2016 presidential election. Considered a close friend and confidant of the US president, Cohen faced criminal charges for his work for Trump. In August 2018 Cohen pleaded guilty to eight counts of campaign finance violations, tax fraud, and bank fraud, admitting that on the eve of the 2016 presidential election he made a $130,000 payment to porn star Stormy Daniels, and arranged for a $150,000 payment to the former Playboy model Karen McDougal. Cohen also admitted lying during campaign about a Trump property deal in Russia. He is one of of five of Trump’s presidential aides to have been found to have broken the law. He was sentenced to three years in prison in December 2018, and was also ordered to pay nearly $2m in fines and restitution requirements. Having previously described himself as “the guy who would take a bullet for the president”, when sentenced, Cohen said “I have been living in a personal and mental incarceration ever since the day that I accepted the offer to work for a real estate mogul whose business acumen that I deeply admired. I know now, in fact, there is little to be admired.” The 52 year old is married with two children, and has, over the years flipped between being a member of both the Democrats and the Republicans. He is expected to report to jail in May 2019. Martin Belam

Photograph: Carlos Barría/X90035

Cohen was preparing for a marathon hearing of the oversight committee, which has 42 members. Republicans keen to defend the president were expected to attack his credibility. Cohen pleaded guilty to crimes including lying to Congress and is scheduled to go to prison in May to begin a three-year sentence.

His prepared remarks painted a scathing picture of a mobster-like president, who denounced Cohen as a “rat” for turning on his former boss. Cohen recalled being dispatched by Trump to shortchange suppliers and to threaten his schools that they must not release his student grades.

Describing his testimony as a step on “path of redemption”, Cohen apologized to Congress for his past lies about the details of Trump’s plans in 2016 to build a tower in Moscow. He also said sorry to the country for “working to hide from you the truth about Mr Trump when you needed it most”.

Cohen described being intoxicated by Trump’s charisma in the early days of their work together. Now, he said, he understood Trump was an unkind, disloyal man in whom “the bad far outweighs the good’”.

Trump said black people were “too stupid” to vote for him and remarked during a drive through a poor area of Chicago that “only black people could live that way,” according to Cohen. “He once asked me if I could name a country run by a black person that wasn’t a ‘shithole’,” Cohen said.