GUANTÁNAMO BAY, Cuba — In announcing last week that the leader of Al Qaeda, Ayman al-Zawahri, had been killed in a U.S. drone strike in Kabul, Afghanistan, President Biden described the long-sought terrorist as “a mastermind” behind the U.S.S. Cole bombing in 2000.

Mr. Biden also said that al-Zawahri was “deeply involved in the planning” of the attacks of Sept. 11, 2001.

There is no doubt that al-Zawahri was the leader of a terrorist movement whose global jihad has killed thousands of people. He was the deputy to Al Qaeda’s founder, Osama bin Laden, and took over the organization in 2011.

But as a matter of historical accuracy, Mr. Biden’s words went well beyond how the government and terrorism specialists have described al-Zawahri’s record with regard to those two particularly notorious attacks.

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.”

The official, who spoke on the condition of anonymity to discuss the sensitive matter, defended Mr. Biden’s characterization of al-Zawahri’s record in relation to the specific attacks as accurate. The Justice Department had charged al-Zawahri, along with Bin Laden and many others, as conspirators in the 1998 bombings of the U.S. embassies in Kenya and Tanzania, the official noted, adding that the government saw “a through line from that to Al Qaeda’s major attacks in 2000, 2001 and beyond.”

During a briefing with reporters shortly before Mr. Biden delivered his remarks, a different senior administration official described al-Zawahri as Bin Laden’s “deputy during the 9/11 attacks,” which is not in dispute. That official did not mention the Cole.

Prosecutors in federal civilian court and in the military commissions system at Guantánamo Bay have filed multiple indictments against Qaeda operatives accused of helping plot the Cole bombing. Those documents are dozens of pages long, laying out the government’s understanding of the participants, meetings, financial transfers and other moves that made up the conspiracy.

They do not portray al-Zawahri as a mastermind of the operation, a suicide bombing by two men in a skiff that killed 17 American sailors.

A Saudi prisoner, Abd al-Rahim al-Nashiri, is described that way in a death-penalty case at Guantánamo Bay. A C.I.A. profile at the time of his transfer in 2006 referred to him as “the mastermind and local manager of the bombing in October 2000.” His charges mention al-Zawahri as one of 26 participants in a Qaeda conspiracy to commit acts of terrorism in general, but not as the mastermind.

A military charge sheet filed in 2012 against five Guantánamo detainees who were accused of conspiring in the Sept. 11 attacks mentioned al-Zawahri only for his joint declaration of war with Bin Laden in 1998, in describing the group’s history.

Within hours of President Biden’s announcement, former President Barack Obama used similar language on Twitter, calling al-Zawahri “one of the masterminds” of the Sept. 11 attacks.

But defense lawyers said the language did not match the descriptions in the case at Guantánamo.

“The 9/11 charges, discovery and proof so far make almost no mention of al-Zawahri,” said James G. Connell III, a capital defense lawyer for Ammar al-Baluchi, the nephew of Khalid Shaikh Mohammed, who is commonly described as their architect of the attack.

The senior military defense lawyer in the Cole case, Capt. Brian L. Mizer of the Navy, said that al-Zawahri figured in pretrial evidence only as a deputy in Al Qaeda, not as someone who had a specific role in the operation.

Ali Soufan, a former F.B.I. agent who investigated Al Qaeda in the period surrounding both attacks, said al-Zawahri was not the operational mastermind of either plot. But as a senior leader, he said, al-Zawahri helped set the strategic direction for Al Qaeda’s major actions during that time.

“He was involved in greenlighting operations and advising Bin Laden,” Mr. Soufan said.

Specifically, Mr. Soufan said, there is evidence that at a council meeting of senior Qaeda leaders, some opposed the Sept. 11 plot, fearing repercussions for their safe haven in Afghanistan, but al-Zawahri backed Bin Laden’s desire to go forward with it.

Emile Nakhleh, a retired senior intelligence service officer and director of the Political Islam Strategic Analysis Program at the C.I.A., said al-Zawahri was absolutely an important target. “We don’t put $25 million on the head of a small fish,” he said.

But he considered al-Zawahri to be more of a “strategic thinker of Al Qaeda.”

The senior administration official who defended Mr. Biden’s remarks also pointed to comments by Kirk Lippold, who commanded the Cole at the time of the attack. Mr. Lippold said on a news program last week that al-Zawahri, along with Bin Laden, had been “intimately involved in the planning.”

But Mr. Lippold, who declined to comment for this article, did not cite any specific basis for portraying al-Zawahri as intimately involved in the planning. In his 2012 memoir about the incident, “Front Burner: Al Qaeda’s Attack on the U.S.S. Cole,” Mr. Lippold mentioned Bin Laden about two dozen times but did not mention al-Zawahri.

Mark Fallon, who was the commander of a Navy task force that investigated the Cole bombing and later oversaw investigations in the military commissions system, said he recalled speculation that al-Zawahri might have been involved in planning both attacks, but he was not aware of evidence supporting a direct link.

“It’s just not a factual narrative that they’re telling,” he said. “It’s a talking point.”