copyright 2009, The Washington Post WASHINGTON -- Investigators on Friday bore down on the possible motives of Maj. Nidal Malik Hasan, the alleged Fort Hood gunman, to determine whether his actions were driven by stress related to his upcoming deployment to Afghanistan or an Islamist political ideology. Law enforcement officials also faced questions about whether they had missed possible warnings signs. Six months ago, investigators came across Internet postings in which Hasan allegedly indicated sympathy for suicide bombers and empathized with the plight of Muslim civilians killed in Iraq and Afghanistan, according to a federal official briefed on the situation. The official, and another source, said investigators never confirmed that Hasan was the author of the postings and did not pursue the matter further. The postings were among a handful of possible red flags that preceded Thursday's rampage, in which Hasan allegedly killed 13 people and wounded nearly 40 others in the deadliest ever mass shooting on a U.S. military installation. Friends and acquaintances said Hasan had been increasingly agitated over the U.S. wars in Iraq and Afghanistan, and he reportedly said the U.S. 'war on terror' was in fact a 'war on Muslims.' Officials have seized Hasan's computer to determine his role in the blog posts and other writings. Investigators cautioned that it was too early to assign a motive to Hasan. Some evidence suggested stress may have played a factor at Fort Hood. Hasan had spent nearly his entire Army medical career at Walter Reed Army Medical Center in Washington D.C., caring for the victims of trauma. Regardless of his motive, lawmakers on Friday expressed puzzlement as to how one of the Army's own could have perpetrated such an attack. Rep. Neil Abercrombie, D-Hawaii, a member of the House Armed Services Committee, said the committee would review how the military can better 'spot troubled personnel like him in the future.' Already, Abercrombie said, the committee has begun examining 'stress factors and psychological preparedness as a major institutional concern.' The shooting has deeply troubled President Obama, who has made repairing U.S. relations with the Islamic world an important element of his foreign policy and who now faces the potential of a public backlash against Muslim Americans. Speaking Friday in the White House Rose Garden, Obama said, 'We don't know all the answers yet and I would caution against jumping to conclusions until we have all the facts.' Hasan's parents came from a Palestinian village not far from Jerusalem, although he was born and raised in the United States. In his blog posts, he allegedly compared suicide bombers to soldiers who fall on grenades to save their comrades. The Federal Bureau of Investigation contends with a heavy volume of Internet comments from white supremacists, religious radicals and other fringe groups. Additionally, under Justice Department guidelines, the FBI cannot open an investigation based solely on a person's speech, even if it demonstrates racist or extremist tendencies. The rules applied to alleged Holocaust museum shooter James von Brunn, whose writings had come to the attention of law enforcement but who was investigated before the deadly attack earlier this year. U.S. authorities have disclosed at least 10 domestic terrorist cases in the last year, the most since 2001. A number of them involved attacks against U.S. military personnel within the United States. In September, federal prosecutors charged two North Carolina men for allegedly conspiring to kill personnel at the U.S. Marine Corps base at Quantico, Va.., seeking to attack U.S. forces at home if they could not overseas. In June, Abdul Hakim Mujahid Muhammad, an American Muslim convert, allegedly shot and killed one soldier and wounded another at a military recruiting center at Little Rock, Ark., in what he said was retaliation for U.S. counterterrorism policies worldwide. Also this year, the last of five men was sentenced in April to 33 years in prison for planning to kill soldiers at Fort Dix, N.J., a plot inspired by foreign terrorist groups. 'I'm not saying it's part of an organized campaign or a systematic strategy, but we're seeing a sea change when we have once-a-month a plot that is related somehow to Afghanistan, Iraq, or what these people see is a war against Islam,' said Bruce Hoffman, professor of security studies at Georgetown University. 'It's too easy to dismiss them as unstable individuals when they have expressed strong religious beliefs with politics.' Fort Hood investigators face a challenge similar to the one that faced by officials after the bombing of the Alfred Murrah Federal Building in Oklahoma City in April 1995. At the time, officials sought to determine if bombers Timothy J. McVeigh, an Army veteran with a distinguished record, and Terry L. Nichols, acted alone, or were part of a larger violent movement. 'I do not know if it is a current or a lasting trend,' Frank Cilluffo, a former Bush White House aide who now leads George Washington University's Homeland Security Policy Institute. 'But obviously it is something we need to be concerned about, because some folks obviously won't be on our radar screen.' The U.S. military's Northern Command did not raise the threat level for U.S. military forces following the Fort Hood attack, keeping it at the lowest level. Northcom spokesman Michael Kuchareck said, 'We looked at it and view it as an isolated incident.' Army Chief of Staff Gen. George Casey said Friday he had asked Fort Hood commanders to review force protection measures after the shootings, which he called 'a kick in the gut.' Army officials said such reviews are ongoing at all installations nationwide, but said there had been no overarching order to raise the level of alert. Security levels at U.S. Army posts are determined by local commanders, although if the Department of Homeland Security changes the nationwide threat level, the Army posts follow suit. Force protection measures at Army installations were tightened significantly in the wake of the Sept. 11, 2001, terrorist attacks, particularly at the entrance to bases. On Army posts, weapons and ammunition used for training, as well as soldiers' private firearms, are stored in fortified rooms. If soldiers live in private housing on the posts, they are required to register personal weapons with the provost marshal, but doing so is left largely up to them. When Hasan was shot, military investigators say, he was armed with at least two personal weapons. Staff Writers Ann Scott Tyson and Ben Pershing contributed to this report. 