A hint that special counsel Robert Mueller is still pursuing the question of whether there was collusion between Donald Trump’s presidential campaign and Russia has emerged during a closed-door hearing.

Comments by one of Mr Mueller’s lead prosecutors, disclosed in a transcript of the hearing in Washington last week, suggest that the special counsel continues to pursue at least one theory about a possible deal between Trump's campaign and Russia.

According to the theory, while Russia was taking steps to bolster Mr Trump’s candidacy, people in his orbit were discussing deals to end a dispute over Russia’s incursions into Ukraine.

It is also thought that they sought to give Moscow relief from economic sanctions imposed by the United States and its allies.

The theory was offered almost as an aside by the prosecutor, Andrew Weissmann, during a discussion of contacts between Mr Trump’s former campaign chairman, Paul Manafort, and a longtime Russian associate, Konstantin Kilimnik. Investigators have linked Mr Kilimnik to Russian intelligence.

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A closer look at the transcript, released on Thursday, shows that the prosecutors have been keenly focused on discussions the two men had about a plan to end the conflict that followed Russia’s invasion of Ukraine and annexation of Crimea in 2014.

Persuading the United States to ease or end the US-led sanctions imposed to punish Moscow for its aggression has been a primary goal of Russian foreign policy.

According to the transcript, which was heavily redacted, Mr Manafort and Mr Kilimnik repeatedly communicated about a so-called peace plan for Ukraine starting in early August 2016. At this point Mr Manafort was still running Mr Trump’s campaign.

This discussion continued into 2018, months after Mr Manafort had been charged by the with a litany of crimes related to his work in the country. The prosecutors claim that Mr Manafort misled them about those talks and other interactions with Mr Kilimnik.

Pressed by the judge at Monday’s hearing to say why Mr Manafort’s alleged lies mattered, Mr Weissmann gave a broad hint about the thrust of the investigation.

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“This goes to the larger view of what we think is going on, and what we think is the motive here,” Mr Weissmann said. “This goes, I think, very much to the heart of what the special counsel’s office is investigating.”

Mr Weissmann’s comments suggest that the special counsel’s investigation is still pursuing the central question of whether there was some kind of deal between Russia and the Trump campaign.