Law enforcement officials also faced questions about whether they had missed possible warning signs. Six months ago, investigators came across Internet postings, allegedly by Hasan, that 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 whether Hasan was the author of the postings and did not pursue the matter…

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 James W. von Brunn, the alleged Holocaust Memorial Museum shooter whose writings had come to the attention of law enforcement but who was not investigated before the deadly attack this year…

“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.”