(CNN) President Donald Trump's former national security adviser and Russia investigation cooperator Michael Flynn will be a "principal witness" in the upcoming trial of his former lobbying partner -- and his statements to special counsel Robert Mueller will matter in that case too, according to court submissions on Friday.

The flood of court requests from the lobbyist Bijan Kian made clear how much of the case will focus on Flynn. Kian's defense team wants every document it can get about the former Trump administration official as they prepare for trial.

Kian's legal team wants "all statements, transcripts, notes, records and memoranda" from federal prosecutors that reflate to anything Flynn said to "any agent, employee, representative or elected official" of the US government.

That includes investigators' memoranda of interviews Flynn gave to Mueller's legal team as they investigated the election and the Trump political operation.

Those notes -- especially about Flynn lying to Vice President Mike Pence and others in the early days of the Trump administration about his contact with Russia regarding sanctions -- could help Kian's lawyers cut into his credibility at trial, Kian's lawyers wrote. They've asked for the Mueller memos on Flynn but the Justice Department won't turn them over as potentially exculpatory material for Kian, the defense team wrote.

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