He was also a co-chair of the United States Justice Department’s nationwide investigation into the September 11 attacks.

Kelley, who served as chief of the organized crime and terrorism unit in the U.S. Attorney's Office for the SDNY, is noted for leading the investigations of the 2000 millennium attack plots and the October 2000 attack on the USS Cole in Yemen, and for prosecuting Ramzi Yousef[3] for his role in the 1993 World Trade Center bombing.

He was named Special Assistant United States Attorney in the Eastern District of Virginia acting as co-lead prosecutor of John Walker Lindh.

Kelley is also noted for obtaining convictions of WorldCom CEO Bernie Ebbers[4] in his prosecution for accounting fraud and Martha Stewart in the ImClone stock trading case.

After leaving the U.S. Attorney's office in 2005, Kelley joined Wall Street law firm Cahill Gordon & Reindel[6] as a partner in its litigation and corporate investigations practice.