Former Acting U.S. Attorney William Weinreb of the District of Massachusetts has joined Quinn Emanuel Urquhart & Sullivan as a partner in Boston.

“I felt that it was time for a new challenge,” Weinreb said Tuesday. “I was attracted by Quinn Emanuel because they're one of the premier white-collar and litigation practices in the country.”

Boston has been an increasingly hot market for Am Law 100 firms, with at least four of them adding offices there in the last year. Quinn Emanuel opened its doors in Boston earlier this year with three IP litigators. Less than a month after its arrival, the firm lured two lawyers away from Ropes & Gray to grow the outpost.

“Our Boston office has grown faster than any office we have ever opened,” said managing partner John Quinn in a statement. “We are pleased to be adding a lawyer of Bill's stature to our white-collar and investigations practice, which is one of the fastest-growing practice areas in our firm.”

Weinreb was the lead prosecutor in the investigation and 2015 trial of Boston Marathon bomber Dzhokhar Tsarnaev. (His fellow prosecutor on the Tsarnaev case, Al Chakravarty, also recently shifted to private practice, joining Snell & Wilmer as a partner in Denver.)

Weinreb said recent departures from U.S. attorneys' offices reflect a normal rate of turnover, adding that no one else was poised to join him in the private sector from the Massachusetts office soon.

Weinreb served nearly 20 years in the Boston U.S. Attorney's Office and was the lead prosecutor in 20 felony jury trials there. After former Massachusetts U.S. Attorney Carmen Ortiz resigned in the early days of the Trump administration in January 2017, Weinreb became the acting U.S. attorney.

The Senate confirmed Andrew Lelling, Trump's nominee for the Massachusetts U.S. attorney's seat, in December 2017.

The white-collar and investigations practice at Quinn Emanuel is co-chaired by Bill Burck, who represents former Trump chief strategist Steve Bannon, former White House chief of staff Reince Priebus, and White House counsel Don McGahn. In an email touting the ”impeccable reputation for excellence and integrity” of the firm's new white-collar hire, Burck did not answer whether Weinreb would assist in those or any other matters related to special counsel Robert Mueller.

“We are very excited that Bill is joining QE,” Burck wrote. “He will immediately be a key member of our global white-collar practice.”

Weinreb noted he looked forward to working on matters of high interest in Boston, particularly involving private equity and life sciences.