WASHINGTON (AP) — Special counsel Robert Mueller says a lawyer for one of Donald Trump’s former campaign aides may have a conflict of interest.

Mueller is investigating possible coordination between the Trump campaign and Russia.

In court papers Monday, he said Walter Mack, the attorney for Rick Gates, may have a conflict. Gates has pleaded not guilty to federal money laundering and other charges for behavior as far back as 2012.

Mack also represents a business associate of Gates who federal prosecutors in New York have charged with bilking movie investors of millions of dollars.

The two cases aren’t related, but Mueller says he’s identified recent financial transactions between the two men.

That’s a potential conflict for Mack, who may someday offer advice to one of his clients that could hurt the other.