Washington ( CNN ) -- A key congressional committee opened its investigation Thursday into the November 5 Fort Hood shootings with a pledge to find out if authorities failed to `` connect the dots '' and could have prevented the attack . The head of the committee promised the inquiry would not interfere with a separate investigation into the shootings being conducted by Defense Secretary Robert Gates and Attorney General Eric Holder . `` Their investigation looks backward and is punitive . Ours looks forward and is preventive , '' said Senate Homeland Security Committee Chairman Joe Lieberman , I-Connecticut , . Maj. Nidal Malik Hasan , a U.S. Army psychiatrist , is accused of opening fire at a military processing center at Fort Hood Army Post , killing 13 people . Dozens of others were wounded . Hasan was shot and paralyzed during the attack and remains in a military hospital . Lieberman said the committee will carry out its investigation `` with respect for the thousands of Muslim-Americans who are serving in the American military with honor and the millions of other patriotic , law-abiding Muslims who live in our country . '' But , he added , `` we do no favor to all our fellow Americans who are Muslim by ignoring real evidence that a small number of their community have , in fact , become violent Islamists and extremists . '' Lieberman said the committee 's investigation will focus on whether concerns raised by Hasan 's colleagues about his `` mental stability and political extremism '' were dealt with appropriately by senior Army officials . Among other things , a memo reportedly written two years ago by Hasan 's supervisor at Walter Reed Army Medical Center says Hasan demonstrated `` a pattern of poor judgment and a lack of professionalism '' during his residency at the hospital . CNN could not corroborate the authenticity of the memo , which was obtained by National Public Radio . Lieberman also said the committee will examine a lack of response by federal authorities after uncovering an exchange of e-mails between Hasan and a radical cleric accused of having ties to al Qaeda . The FBI has said it was aware of communication between Hasan and Anwar al-Awlaki , a Yemeni-American cleric who has promoted jihad against the United States and other Western countries . But investigators determined that those contacts were `` consistent with research being conducted by Maj . Hasan . '' Also , Lieberman noted , the committee will look into whether information on Hasan gathered by a joint terrorism task force was shared with officials in the Army , the Defense Department or elsewhere . Maine Sen. Susan Collins , the ranking Republican on the committee , said Hasan 's case `` raises questions about whether or not restrictive rules have a chilling effect on the legitimate dissemination of information , making it too difficult to connect the dots that would have allowed a clear picture of the threat to emerge . '' But a law enforcement official familiar with the investigation told CNN that when Hasan first came to the attention of investigators because of his communications with al-Awlaki , officials looked at his military personnel file and nothing was found that raised suspicion . None of the items that have been reported since the shootings -- including the reported memo from his Walter Reed supervisor or a Power Point presentation arguing that Muslims in the Army should be given conscientious objector status -- were part of the file , the official said , but it was noted that Hasan had done research about Muslims in the military . Thursday 's hearing included testimony from former Army Vice Chief of Staff Gen. John Keane , Rand Corp. consultant Brian Jenkins and New York City Police Department intelligence analyst Mitchell Silber . `` At a glance , Maj. Hasan 's rampage at Fort Hood looks a lot like what used to be called 'going postal , ' `` Jenkins said . It was `` a deepening sense of personal grievance culminating in a homicidal rampage directed against co-workers -- in this case , fellow soldiers . `` For Hasan , 'going jihad ' reflects the channeling of obvious personality problems into a deadly fanaticism , '' he said . The committee launched its investigation only hours before Gates announced a 45-day review of Pentagon policies to see if the Defense Department has fallen short in identifying service members `` who could potentially pose credible threats to others . '' The review will be led by former Army Secretary Togo West and retired Adm. Vern Clark , a former Navy chief . At the same time , the Army will conduct its own , more detailed review of its policies and whether they could have prevented the shootings at the post in Texas . And those will be followed by a four- to six-month study of `` systemic institutional shortcomings '' conducted by each of the armed services . The Fort Hood shooting has `` broader implications for society ... particularly in these lone wolf cases , which are the hardest , '' Lieberman said . `` When people hear people saying things that seem extreme ... respecting First Amendment rights , you 've got to begin to reach out and see if you can stop somebody before they do something very harmful . ''
Incident has `` broader implications for society , '' Sen. Joe Lieberman says . Congressional committee opens inquiry into massacre at Fort Hood , Texas . Lieberman : Feds ' lack of response after uncovering e-mails will be examined . Also to be investigated is whether task force information about suspect was shared .