The American Lawyer reports US Attorney Thomas O'Brien has taken on international drug cartels, some of the West Coast's toughest street gangs, and human smuggling rings. But now he has to do something that may be even more challenging: build a book of business.

Paul, Hastings, Janofsky & Walker announced Tuesday that O'Brien, who has been US Attorney for the Central District of California since 2007, will become a partner in the firm's Los Angeles office, where he will focus on white-collar cases.

"The people I met at Paul Hastings are top notch attorneys and I look forward to working with the firm to help them develop a white-collar practice in Los Angeles," says O'Brien, who was appointed US Attorney by President George W. Bush after more than two years as the office's criminal division chief.

He joins the firm Oct. 1.