UPDATE Monday, March 8: As more information emerges about Mr. Bedell, the less it appears that any coherent ideology was behind his actions, except that he was deeply antigovernment. The Monitor has changed the headline, subhead, and first paragraph of this story, which originally suggested a right-wing motive.

John Patrick Bedell, whom authorities identified as the gunman in the Pentagon shooting on Thursday, appears to have been an extremist with virulent antigovernment feelings.

If so, that would make the Pentagon shooting the second violent extremist attack on a federal building within the past month. On Feb. 18, Joseph Stack flew a small aircraft into an IRS building in Austin, Texas. Mr. Stack left behind a disjointed screed in which, among other things, he expressed his hatred of the government. (For more on this incident, click here.)

Details of Mr. Bedell’s case are still emerging. But writings by someone with his same name and birth date, posted on the Internet, express ill will toward the government and the armed forces and question whether Washington itself might have been behind the Sept. 11 terrorist attacks.

However, law enforcement officials have yet to publicly state their theories as to Bedell’s motives.

“I have no idea what his intentions were,” said the chief of Pentagon police, Richard Keevill, in a Friday press conference.

According to Mr. Keevill, Bedell was a California native who slowly made his way to Washington by car over the past several weeks.

At about 6:40 p.m. on Thursday, Bedell, dressed in a business suit, approached an entrance to the Pentagon that is linked to the Washington’s Metro system. Asked for identification, he pulled out a semiautomatic weapon and opened fire.

At that time of day, that particular Pentagon entrance is teeming with people, as it is a main connection with both subway and buses and with the building’s vast commuter parking lots. Because of this, it is one of the most fortified points of a fortified building. Bedell would have had to make his way past several lines of security to reach the Pentagon interior.

He did not get far. Two officers immediately returned fire, with a third running to their assistance.

Bedell was fatally wounded in the exchange. Two officers were wounded but have since been released from the hospital.

“He just reached in his pocket, pulled out a gun, and started shooting” at point-blank range,” Pentagon police chief Keevill said. “He walked up very cool. He had no real emotion on his face.”

According to the Associated Press, an Internet posting made by someone using the name JpatrickBedell expressed a determination to see justice served in the case of Marine Col. James Sabow, who was found dead in his California home in 1991. Authorities have ruled this case a suicide, but it has become a cause célèbre among extremists who consider that ruling a coverup by the government.

The posting expressed general hatred of Washington and added that exposing the Sabow case would be “a step toward establishing the truth of events such as the September 11 demolition,” according to the AP.

The Pentagon attack and the destruction at the IRS building in Austin, Texas, come at a time of explosive growth in extremist-group activism across the United States, according to the Southern Poverty Law Center, which tracks such organizations.

The number of US extremist paramilitary militias grew from 42 in 2008 to 127 in 2009, according to a just-released SPLC annual report.

So-called “Patriot” groups, steeped in antigovernment conspiracy theories, grew from 149 in 2008 to 512 in 2009 – an increase that the SPLC report judges as “astonishing.”