Lieberman wanted to hear from FBI officials about missed signals that Nidal Malik Hasan exhibited radical viewpoints and created concern among his colleagues.
But the administration didn't allow any current government witnesses, in deference to the ongoing criminal investigation.
According to the Washington Post, Lieberman said conversations with Attorney General Eric Holder and Defense Secretary Robert Gates left him optimistic that the committee would gain access to some of the information it is seeking soon.
Thursday, the committee heard testimony on how to better identify potential radicals in the armed forces and how to empower people to report their concerns up the chain of command, even when the concerns involved an officer like Hasan.
Among the witnesses were retired Gen. John Keane, a former Army vice chief of staff; Frances Fragos Townsend, President George W. Bush's homeland security adviser, and terrorism expert Brian Michael Jenkins of the RAND Corp.
The New York Times reported that the Pentagon was initiating a review of the Hasan case that would have a similar focus.
The Investigative Project on Terrorism covered the hearing and prepared a video summary below: