A Russian analyst who played a major role in the creation of a flawed dossier about Donald Trump fabricated one of his own sources and concealed the identity of another when interviewed by the FBI, prosecutors said Tuesday.

The allegations were aired during opening statements in the trial of Igor Danchenko, who is indicted on five counts of making false statements to the FBI.

The FBI interviewed Danchenko on multiple occasions in 2017 as it tried to corroborate allegations in what became known as the “Steele dossier”.

That dossier, by the British spy Christopher Steele – commissioned by Democrats during the 2016 presidential campaign – included allegations of contact between the Trump campaign and Russian government officials, as well as allegations that the Russians may have held compromising information over Trump in the form of videos showing him engaged in salacious sexual activity in a Moscow hotel.

Specifically, prosecutors say, Danchenko lied when he said he obtained some information in an anonymous phone call from a man he believed to be Sergei Millian, a former head of the Russian American Chamber of Commerce.

The prosecutor Michael Keilty told jurors in US district court in Alexandria that Danchenko had never spoken with Millian and that phone records showed he had never received an anonymous phone call at the time Danchenko claimed it occurred.

Prosecutors also say Danchenko lied when he said he never “talked” with a man named Charles Dolan about the allegations contained in the dossier. Prosecutors say there is evidence that Danchenko “spoke with Mr Dolan over email” about very specific items that showed up in the dossier.

The FBI needed to know that Dolan was an important source for Danchenko, Keilty said, because Dolan is a Democratic operative who has worked on the presidential campaign of every Democratic candidate since Jimmy Carter, and thus would have had motivation to fabricate or embellish allegations against Trump.

“Those lies mattered,” Keilty said.

But Danchenko’s attorney, Danny Onorato, told jurors that his client had been completely truthful with the FBI.

He pointed out that Danchenko had never said he was certain that Millian was the source of the anonymous call but that he had good reason to believe it. The government’s case required jurors to become “mind readers” to assess Danchenko’s subjective belief about the source of the phone call, Onorato said.

And while phone records might not show a call, Onorato said, the government had no idea whether a call could have been placed with a mobile app rather than a traditional telephone provider. Indeed, Onorato said, it made more sense that such a call would have occurred using an internet app because so many of them conceal the source of the call, and the caller wanted to be anonymous.

As for the allegations about his discussions with Dolan, Onorato said, Danchenko had answered the question truthfully because the two had not “talked” – but rather had conducted a written exchange. If the FBI had wanted to know about email exchanges, it should have asked a different question, Onorato said.

“The law doesn’t let you rewrite the dictionary,” Onorato said.

Keilty, in his opening, acknowledged to jurors that evidence would show the FBI made errors in conducting its investigations, but he said that shouldn’t exonerate Danchenko.

“A bank robber doesn’t get a pass just because the security guard was asleep,” Keilty said.

The first prosecution witness was the FBI analyst Brian Auten, who testified that information from the Steele dossier had been used to support a surveillance warrant against a Trump campaign official, Carter Page.

Under questioning from Durham, Auten testified that the dossier had been used to bolster the surveillance application even though the FBI couldn’t corroborate its allegations.

Auten said the FBI had checked with other government agencies to see if they had corroboration but nothing had come back. Auten and other FBI agents had even met with Steele in the United Kingdom in 2016 and offered him as much as $1m if he could supply corroboration for the allegations in the dossier, but none had been provided.

Danchenko is the third person to be prosecuted by the special counsel John Durham, who was appointed to investigate the origins of “Crossfire Hurricane” – the designation given to the FBI’s 2016 investigation into Trump’s Russia connections. It is also the first of Durham’s cases that delves deeply into the origins of the dossier, which Trump derided as fake news and a political witch-hunt.