WASHINGTON -- The finger-pointing began in earnest on Wednesday over who in the alphabet soup of American security agencies knew what and when about the Nigerian man charged with trying to blow up an airliner.

But the harshest spotlight fell on the very agency created to make sure intelligence dots were always connected: the National Counterterrorism Center. The crown jewel of intelligence reform after the Sept. 11, 2001, attacks, the center was the hub whose mission was to unite every scrap of data on threats and suspects, to make sure an extremist like Umar Farouk Abdulmutallab, the would-be bomber, would never penetrate the United States’ defenses.

“N.C.T.C. is supposed to be the nerve center,” said Amy B. Zegart, who studies intelligence at the...