Once a month, a group of staff members from the House and Senate intelligence committees drives across the Potomac River to CIA headquarters in Virginia, assembles in a secure room and begins the grim task of watching videos of the latest drone strikes in Pakistan and Yemen.
Sometimes, they see Hellfire missiles hit buildings after suspected terrorists have entered. Other times, they can make out a group or a vehicle consumed in a fiery blast. Occasionally, a smaller explosion kills just one person, as officials say happened when a missile this month crashed into a room in Pakistan's tribal areas and killed Abu Yahya al-Libi, al-Qaida's No. 2.
The videos are much sharper than the grainy drone imagery that can be viewed on the Web. "You can see exactly what is going on," said a senior congressional aide, who, like other officials, spoke about the highly classified program on condition that he not be identified.
The regular review of some of the most closely held video in the CIA's possession is part of a marked increase in congressional attention paid to the agency's targeted killing program over the last three years.
The oversight, which has not previously been detailed, began largely at the instigation of Sen. Dianne Feinstein, D-Calif., who chairs the Senate Intelligence Committee, officials said.
The lawmakers and aides with the intelligence oversight committees have a level of access shared only by President Barack Obama, his top aides and a small number of CIA officials.
In addition to watching video, the legislative aides review intelligence that was used to justify each drone strike. They also sometimes examine telephone intercepts and after-the-fact evidence, such as the CIA's assessment of who was hit.
"We receive notification with key details shortly after every strike, and we hold regular briefings and hearings on these operations," Ms. Feinstein wrote in May, in a letter sent in response to a column in the Los Angeles Times questioning oversight of drone strikes.
"Committee staff has held 28 monthly in-depth oversight meetings to review strike records and question every aspect of the program including legality, effectiveness, precision, foreign policy implications and the care taken to minimize noncombatant casualties."
Ms. Feinstein did not respond to requests for an interview.
The United States faces international criticism for its drone strikes. Officials in Pakistan, in particular, have complained that strikes have killed many civilians, and some members of Congress have recently raised questions about "signature" drone attacks based on an individual's pattern of behavior.
Congressional officials say their review has made the CIA more careful. They are hard-pressed, however, to point to any changes the agency has made. The CIA declined to comment...