"This is the highest value target we have captured in years," Sen. Saxby Chambliss (R-Ga.), vice chairman of the Senate intelligence panel, said during the same press briefing.
During Tuesday's briefing, Graham noted that U.S. intelligence have said al-Libi was in Libya for two years prior to the strike on the diplomatic annex.
That said, "there is almost zero chance" the he does not have information on, or possibly played a role in planning the deadly assault, according to Graham.
But the White House is sacrificing the opportunity to get that intelligence by opting not to transfer al-Libi to the military prison in Guantánamo Bay, Cuba.
U.S. military and intelligence officials are interrogating al-Libi aboard a Navy warship in the region before remanding him into federal custody to stand trial.
Al-Libi was indicted in absentia by a federal court in the southern district of New York for his alleged involvement in the bombings of the U.S. embassies in Dar es Salaam, Tanzania, and Nairobi, Kenya, in 1998.
But under the rules of war, al-Libi can only be held for up to 60 days aboard the Navy ship before being handed over to the Justice Department.
That is simply not enough time to uncover the valuable intelligence gained by al-Libi during his decadeslong involvement with al Qaeda, Graham said.
"The best tool for an interrogator is time," Graham said.
"When you take time off the table ... you are [aiding] the enemy," he added.
If al-Libi were turned over to U.S. military forces in Cuba, interrogators would have time to find out exactly what he knows about Benghazi and other terror plots, Chambliss said.
"Some folks have been in [Guantánamo] for 10 years, and we are still getting information from them," he added.
But Sen. Kelly Ayotte (R-N.H.) accused the White House of making a "political decision" to keep al-Libi out of Cuba, sacrificing the intelligence opportunity he provides.
"If we lose the opportunity to get that information ... [that] is an absolutely unacceptable outcome," Ayotte said. "Our nation deserves better."