Mary Beth Buchanan, who served eight years as U.S. Attorney of Western Pennsylvania, is joining Bryan Cave as a partner focusing on white-collar defense, securities litigation and enforcement practices. Buchanan, 50, will work primarily in New York.

Buchanan said she spoke with at least half a dozen law firms about her move to private practice, but said 1,000-attorney Bryan Cave, based in St. Louis, stood out. As companies aim to bolster their compliance programs, Buchanan said she’ll focus on corporate compliance, internal investigations, white collar defense, foreign corrupt practice violations and health care fraud.

“I felt very comfortable with the size of Bryan Cave. This practice group is already established but it’s still growing,” Buchanan said. “With some firms that already had a huge white-collar practice, it may have been more difficult for me to integrate.”

Buchanan was director of the Executive Office for U.S. Attorneys in 2004 and 2005. She served as U.S. Attorney for the Western District of Pennsylvania from 2001 to 2009, overseeing the prosecution of more than 5,000 cases.

Among her more controversial cases were the prosecution of actor Tommy Chong, who pleaded guilty to conspiring to sell drug paraphernalia; and the prosecution of medical examiner and prominent Democrat, Cyril Wecht. A hung jury led to dismissal of corruption charges in what some critics alleged was a politically motivated case. Buchanan said she doesn’t believe the controversy will follow into private practice. “If people are only talking about two cases” among more than 5,000, she said, “that’s pretty good.”

Buchanan ran unsuccessfully for Congress in 2010 and served as ethics and reputational risk officer at the United Nations.