Mr. Biden’s portrayal of al-Zawahri as a key plotter of the Sept. 11 attacks was echoed in many news accounts about his speech, including in The New York Times. But it surprised counterterrorism experts, as did the characterization of al-Zawahri’s role in the Cole bombing.

The remarks also raised new questions in the Sept. 11 and U.S.S. Cole death-penalty cases, which have been mired in pretrial hearings for more than a decade. By Friday, lawyers in both cases said they had formally requested evidence from prosecutors to support Mr. Biden’s statements.

Marc Sageman, a former C.I.A. officer who worked with Islamist fighters battling the Soviet occupation of Afghanistan in the 1980s and later wrote several books about terrorism networks and radicalization, said he was puzzled by Biden’s portrayal of al-Zawahri and wondered where the purported role came from.

“Zawahri is a legitimate target,” he said on Tuesday, a day after the president’s address. “But the justification they gave yesterday was inaccurate. I doubt it. I strongly, strongly doubt it.”