Moves Signal Tighter Secrecy Within C.I.A. By SCOTT SHANE and MARK MAZZETTI WASHINGTON, April 23 — The crackdown on leaks at the Central Intelligence Agency that led to the dismissal of a veteran intelligence officer last week included a highly unusual polygraph examination for the agency's independent watchdog, C.I.A. Inspector General John L. Helgerson, intelligence officials with knowledge of the investigation said on Sunday. The special polygraphs, which have been given to dozens of employees since January, are part of a broader effort by C.I.A. Director Porter J. Goss to re-emphasize a culture of secrecy. As the inspector general, Mr....