BY ERIC TUCKER

Associated Press

WASHINGTON

James W. McJunkin, a former state trooper who rose through the ranks of the FBI while developing an expertise in counterterrorism, alerted colleagues to his departure in an email.

McJunkin has overseen regional investigations into terrorist plots, including a foiled plan to blow up the U.S. Capitol, violent crime and government corruption since being named the office's assistant director in charge in November 2010. But he carved out a national profile in the past decade for his work on some of the most significant counterterrorism investigations in the U.S. and overseas, such as a plot to blow up the New York City subway system, deadly coordinated attacks in Mumbai in 2008 and a suicide bomb attack outside the U.S. consulate in Pakistan.

His departure leaves a void in an agency that considers terrorism investigations its top priority and that has recently lost several top officials with expertise in the area, including former New York office head Janice Fedarcyk, who retired in August.

McJunkin joined the FBI as a special agent in 1987 after starting his law enforcement career with the Pennsylvania state police. He worked in field offices in San Antonio and Atlanta before being promoted to an assistant section chief of the FBI's International Terrorism Operations Section, where he supervised counterterrorism operations. He later led the Washington field office's Joint Terrorism Task Force and ran its counterterrorism division.

Besides terrorism, McJunkin has also presided in the last year and a half over an ongoing investigation into D.C. government corruption. The probe has already wrung guilty pleas from two former Council members and several campaign aides to Mayor Vincent Gray. An investigation into the mayor's 2010 campaign is also continuing.

In his current position, McJunkin can regularly be seen collaborating with his agents and representatives from other law enforcement agencies.