New York City ? An American man charged with giving al-Qaida information on the New York transit system and attacking a U.S. military base in Afghanistan has been a secret witness in the fight against terror here and overseas, authorities revealed Wednesday.

His revelations have given counterterrorism investigators a rare look at the day-to-day operations of al-Qaida — from meetings of top terror officials to training with explosives — in the lawless region bordering Pakistan, which the U.S. military has struggled to penetrate, people familiar with the case said.