Story highlights At this stage, with Gates' charges filed and bail set, talks could concern the charges and Gates' plea

The defense and prosecution are currently working together on discovery of evidence

Washington (CNN) Former Trump campaign aide Rick Gates has quietly added a prominent white-collar attorney, Tom Green, to his defense team, signaling that Gates' approach to his not-guilty plea could be changing behind the scenes.

Green, a well-known Washington defense lawyer, was seen at special counsel Robert Mueller's office twice last week. CNN is told by a source familiar with the matter that Green has joined Gates' team.

Green isn't listed in the court record as a lawyer in the case and works for a large law firm separate from Gates' primary lawyers.

Green's involvement suggests that there is an ongoing negotiation between the defendant's team and the prosecutors. At this stage, with Gates' charges filed and bail set, talks could concern the charges and Gates' plea. The defense and prosecution are currently working together on discovery of evidence.

Gates pleaded not guilty in October to eight charges of money laundering and failing to register foreign lobbying and other business . His longtime business partner, former Trump campaign chair Paul Manafort, pleaded not guilty to nine counts in the same case as Gates.