There was "no indication at this point [of] any domestic or international terrorism at all," he said.
Police also confirmed today that a second individual taken into custody was only briefly detained and was released after authorities determined that he had nothing to do with the incident.
This is not the first case of a fatal Pentagon shooting. In the late 1980s, a person with mental issues came to the Pentagon and shot a Naval officer, but "that was many years ago, before 9/11," Keevill said.
Sources say authorities will look at whether the federal government and the military are increasingly becoming a target.
Just a few weeks ago, Joe Stack flew his plane into the IRS office in Austin, Texas, after leaving a lengthy manifesto in which he told the IRS to "take my pound of flesh and sleep well."
In November, Army Maj. Nidal Hasan went on a shooting rampage in Fort Hood, Texas, after railing on the Internet about the United States' foreign policies and wars in Iraq and Afghanistan.
ABC News' Mary-Rose Abraham, Luis Martinez, Richard Coolidge, Sarah Netter and Ned Potter contributed to this story.