In an email, Justice Department spokeswoman Sarah Isgur Flores said ethics officials had reviewed the case and "determined that Mr. Mueller's participation in the matters assigned to him is appropriate." She said the officials had considered Mueller's professional obligations and those imposed by government ethics regulations.
Mueller, a former FBI director, had worked for the past three years in the Washington office of WilmerHale, a prominent law firm whose lawyers represent President Trump's former campaign chairman Paul Manafort, Trump's daughter Ivanka and the president's son-in-law, Jared Kushner. Mueller resigned from the firm after Deputy Attorney General Rod J. Rosenstein appointed him last week to oversee the investigation of Russian meddling in the election.
But Mueller still had possible conflicts because of his association with the firm, and the Justice Department said at the time it would have to review them. Under a federal ethics regulation, government officials are barred from participating in matters involving their former employers for a year, unless they receive a waiver to do so.
In addition, professional responsibility rules prohibit lawyers from representing a client and then later using information they have learned through that work against the client.
Bruce M. Berman, WilmerHale's general counsel, told The Washington Post last week that Mueller had no involvement in the representation of Manafort, Kushner or Ivanka Trump, or any client in connection with any Russia-related inquiry.
Flores said Mueller and his team would work out of the Patrick Henry Building on D Street NW. It is unclear to what extent he will keep current investigators and prosecutors on the case or replace them with his own team. WilmerHale lawyers James Quarles and Aaron Zebley also stepped down from WilmerHale last week, and a firm spokesman said they were expected to join Mueller.