It was a brief exchange, held in the Oval Office a few weeks after Donald Trump became the 45th president of the United States.

But the meeting between the now ex-president and his former lawyer Michael Cohen could prove pivotal in the criminal case against Mr Trump that is currently playing out in a high-profile New York trial.

"I was sitting with President Trump and he asked me if I was OK, he asked me if I needed money," Mr Cohen testified at the trial on Tuesday.

He said he told the then-president he was "OK", to which Mr Trump responded: "Alright, just make sure you deal with Allen [Weisselberg]". Mr Weisselberg was the Trump Organization's Chief Financial Officer at the time.

Then, Cohen testified, Mr Trump told him a cheque would be coming soon.

After the meeting, Cohen posed for a photo behind the famous lectern in the White House briefing room.

On Tuesday, that snapshot of the man who once said he'd take a bullet for Mr Trump, in a black suit and standing at the press secretary's podium, flashed up on courthouse television screens as evidence in the first-ever criminal trial of a former US president.

Prosecutors also showed an email from a White House aide confirming the meeting.

Mr Trump denies dozens of charges of falsifying accounts to hide a hush-money payment made to adult-film actress Stormy Daniels, who claims they had a sexual encounter, in the lead-up to the 2016 presidential election.

According to prosecutors, Cohen made the payment and was then reimbursed in monthly instalments disguised as legal fees. They say that Mr Trump's alleged hiding of the purpose of the reimbursements was election interference.

The court heard that after the meeting, cheques reimbursing Cohen for the $130,000 (£103,000) he paid to Ms Daniels started to arrive, some with Mr Trump's signature.

Cohen's invoices for these $35,000 monthly cheques were marked as "services rendered".

But speaking in front of a courthouse packed with media and members of the public, Mr Cohen said the invoices were false. He testified they were really to reimburse him for the hush money, with extra dollars added in to cover potential taxes.

These documents - 11 cheques, 11 invoices and 12 entries in an accounts ledger - make up the 34 felony counts charged against Mr Trump of falsifying business records.

Former Manhattan prosecutor Rebecca Roiphe told BBC News that the Oval Office meeting could be a key moment of the trial, but it depends on how credible the jury finds Mr Cohen, who has pleaded guilty to federal crimes, including campaign finance violations and lying to Congress.

"The prosecution could have established its case without Michael Cohen's testimony about the in-person meeting in the Oval Office, but it certainly helps connect the dots," Ms Roiphe said.

"If the jury believes this part of Cohen's testimony, it would completely undermine one of the key defences - that Trump had nothing to do with these payments."

But Mr Cohen's history of lying to Congress, and his time in prison, in part related to paying hush money, are significant factors the jury will have to weigh up.

During two hours of cross-examination of Cohen on Tuesday, Trump's legal team did not touch on his assertions that Trump knew of the hush-money payment and the alleged reimbursement plan. Instead, they worked to dismantle his credibility.

Ms Roiphe said the defence may keep up that line of attack in trying to counter the Oval Office claims when they resume questioning Cohen on Thursday.

"The defence has sought to portray Cohen as a spurned underling who was obsessed with Trump and would stop at nothing to exact revenge," Ms Roiphe said. " It can draw on this theme to try to make it seem as if this uncorroborated testimony is made up."

And indeed that is exactly how this trial began, when Mr Trump's lawyer Todd Blanche's opening statement said this of Mr Cohen:

"He's a convicted felon and a convicted perjurer - he's an admitted liar".