Program Note: Tune in tonight for more on religious preference in the military and whether or not certain red flags regarding Mah. Hasan were ignored. 10 p.m. ET.

AC360°

People who knew and studied Maj. Nidal Hasan say he was a loner who had no luck finding a wife, and a criminal profiler said the Fort Hood shooting suspect fits the profile of a mass murderer better than that of a terrorist.

Investigators are searching for any missed "red flags" that might have prevented last week's fatal shooting, which left 12 soldiers and one civilian dead and 40 other people wounded. However, the FBI has said its investigations indicate the "alleged gunman acted alone and was not part of a broader terrorist plot."

"A lot of people are jumping to the conclusion because this man spouted violent Islamic ideology that this is a terrorist attack," criminologist Pat Brown said.

Since last week's shooting at Fort Hood, Pentagon officials are faced with difficult questions regarding religious affiliation among the ranks.

Pentagon statistics compiled in August of this year show that there were 3,409 Muslims in the active-duty military. But since military personnel have no obligation to disclose their religion, many officials believe the actual number of Muslim soldiers could be at least 10, 000 higher than the Pentagon statistics.

Maj. Nidal Malik Hasan, for instance, did not identify with a specific religion on his military record. This made us wonder about the breakdown of religious preference in the military.

More than one quarter of the personnel (26.3%) are identified as having indicated no religious preference or unknown.

Source: U.S. Department of Defense