WASHINGTON (AP) — The Justice Department official leading the investigation of big tech companies' market dominance is stepping aside from the department's Google probe because of his previous lobbying work for Google as a private attorney.

Assistant Attorney General Makan Delrahim, the department's antitrust chief, is recusing himself from the investigation into Google, a person familiar with the matter said Tuesday. The person wasn't authorized to discuss the investigation and spoke to The Associated Press on the condition of anonymity.

Delrahim lobbied on Google's behalf in 2007 when the Mountain View, California-based internet company faced antitrust scrutiny over its acquisition of DoubleClick, a competitor in digital advertising.

The Justice Department's ethics office apparently found no potential conflict of interest when Delrahim sought guidance as the investigation of Facebook, Google, Amazon and Apple began last spring. But as the competition probe progressed, Delrahim "revisited" potential conflicts with the ethics staff, and he and the ethics office "have decided that he should now recuse himself from a matter within the tech review in an abundance of caution," said a department statement, which did not mention Google.

Associate Deputy Attorney General Ryan Shores will continue to oversee the tech review, the statement said.

Scrutiny of Big Tech has deepened and widened across the federal government, U.S. states and abroad. The Federal Trade Commission also is conducting a competition investigation of the four tech giants, and state attorneys general from both major political parties have opened antitrust probes of Google and Facebook.

The House Judiciary subcommittee on antitrust has been conducting a sweeping bipartisan investigation of the big tech companies and their impact on competition and consumers.

Delrahim has suggested in speeches that he's taking a broad view of how competition is harmed, when assessing whether big tech firms should be broken up. He also has made clear that he is aware that just two companies dominate digital advertising, though he hasn't named the two, Google and Facebook.

Justice Department and FTC officials haven't publicly named the companies under investigation or indicated whether they plan to move against any particular company.

The companies have said they'll fully cooperate with the investigations. But in congressional testimony, their executives have pushed back against accusations that they operate as monopolies, laying out ways in which they say they compete fairly yet vigorously against rivals in the marketplace.

Delrahim's recusal was first reported by The New York Times.