Washington (CNN) Kyle Freeny and Brandon Van Grack, two prosecutors who worked on Paul Manafort's criminal cases, are ending their tenure working for special counsel Robert Mueller.

Van Grack left recently to return to his job in the National Security Division of the Justice Department, and Freeny will leave the office in mid-October to return to the Criminal Division. Both were detailed to Mueller's office over the past year, said special counsel spokesman Peter Carr.

Carr would not say whether this indicated that the office was winding down its efforts, as President Donald Trump's lawyers have suggested and several others who've been in contact with the office have speculated. He said the departures were not for any disciplinary reason.

The two departures, which leave 13 prosecutors under Mueller (nine detailed from the other Justice Department offices and four that he hired directly), suggest that Mueller's efforts have turned a corner with Manafort's cooperation and that other parts of the department will play greater roles in open cases related to Russia's interference in the 2016 election.

Carr declined to comment Tuesday on whether new lawyers would be added to the special counsel's office. Previously, a lawyer who was hired after his Supreme Court clerkship into the office left for a law school fellowship, while another Justice Department prosecutor, cybersecurity specialist Ryan Dickey, stopped regularly assisting the Mueller team.

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