Sharis A. Pozen, the acting head of antitrust at the Justice Department, is leaving the agency to return to practice private law, according to a government official.

Pozen will leave the agency at the end of April. The lead candidate to succeed her is William Baer, an attorney at Arnold Porter in Washington and former head of the antitrust division of the Federal Trade Commission, according to the official, who spoke on the condition of anonymity because the announcement had not been made public.

Pozen was appointed acting attorney general for the antitrust division in August, replacing Christine Varney. Pozen is known for her bold decision to reject AT&T’s $39 billion merger with T-Mobile, saying the merger would harm competition and lead to higher cell phone bills for consumers.

Under Pozen, the Justice Department has also begun an investigation of Verizon Wireless’ purchase of wireless network spectrum from cable companies including Comcast and Time Warner Cable. A person familiar with the agency’s review said the companies’ co-marketing agreement has raised concerns that the deal could lead to less competition.

Pozen joined the Justice Department in 2009 from law firm Hogan & Hartson LLP, where she served as a director of the firm’s antitrust practice.


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