Special Counsel Robert Mueller has enlisted four assistant U.S. attorneys for the case against 13 Russians and three companies, a sign that he may be preparing to hand off part of his Russia investigation to outside prosecutors and finish up his probe into Russian interference in the 2016 presidential election, The Washington Post reports.

Mueller’s office in mid-February charged the 13 Russians and three companies with an elaborate plot to interfere in the election through social media propaganda aimed at helping Republican Donald Trump. The intent of the meddling, the indictment said, was to \"sow discord in the U.S. political system, including the 2016 presidential election.\"

But that case could drag on for years, and Mueller’s team is readying for the July trial against Trump’s ex-campaign chairman Paul Manafort, who has been charged with bank fraud and lobbying violations.

In a pair of court filings Friday, the special counsel added the four prosecutors to the case, and people familiar with the decision told the Post it was done so that they could potentially take over the Russia troll case when Mueller is finished with his investigation.

Mueller on Friday also asked a judge for a September sentencing for former Trump campaign adviser George Papadopoulos, who last year pleaded guilty to making false statements to FBI agents about his contacts with pro-Russia sources during the election.

The Post last week reported that Mueller was aiming to finalize his obstruction report on Trump by the end of the summer, but is still looking for an interview with the president as the last step. The Mueller probe has been ongoing since May 2017, and so far four Trump campaign associates have been charged – former national security adviser Michael Flynn, Manafort, Papadopoulos and Richard Gates. None of the charges, though, are directly related to any misconduct by the president’s campaign.