The lone gunman captured alive in Mumbai has told interrogators only 10 of the 24 young men in his year-long terrorist training course were sent to Mumbai last week, leaving 14 still in Pakistan, ready to strike again, law enforcement and security sources tell ABCNews.com.
Security officials say they have been warned by Indian and U.S. officials that a second attack on the Indian capital city New Delhi is possible.
U.S. officials say the captured gunman's account corroborates other intelligence that points to the role of the Pakistani-based Lashkar e Taiba, a group affiliated with al Qaeda that opposes Indian rule over the disputed state of Kashmir.
U.S. counter-terrorism officials say Lashkar e Taiba's ability to operate with impunity inside Pakistan is one reason U.S. Secretary of State Condoleezza Rice has warned Pakistan "this is a time for complete, absolute, total transparency and cooperation."
A warning issued by U.S. intelligence agencies to Indian officials in mid-October suggests the U.S. may know the precise location of the training camps or headquarters in Pakistan, according to sources in the intelligence community.
"There's going to have be retaliation, but it could be a while," said former CIA intelligence officer John Kiriakou, an ABC News consultant.
"The location of those bases is the worst kept secret in South Asia, but by now they probably have been abandoned," he said.
Mohammad Ajmal Amir Iman, 21, captured by police at Mumbai's main train station, reportedly told interrogators he began training for last week's deadly attack in late 2007 along with 23 other recruits to Lashkar e Taiba, a terror group affiliated with al Qaeda.
He reportedly described four, three-month training segments at locations in Pakistan: physical fitness, running, weapons and explosives and sea maneuvers.
The captured terrorist described his trainers as former Pakistani military officers, including one who was known as Cha-Cha, or Uncle.
Indian officials say his account is corroborated by evidence recovered from the group's boats and from intercepted satellite phone conversations that have been recovered from data files.
The officials say they have now heard one conversation in which a gunman is heard telling Lashkar e Taiba headquarters, "We finished off the four goats," a reference to the murder of four crewmen on the boat hijacked by the attackers in Indian waters.