Updated at 11:37 a.m. ET
A law enforcement source told CBS News that the man detained in the discovery of a suspicious car found outside the Pentagon Friday morning was carrying a notebook that contained the phrases, "al Qaeda," "Taliban rules" and "Mujahid defeated croatian forces."
Despite the references to the terror organization that organized the 9/11 attacks, the group fighting U.S. forces in Afghanistan and the Arabic word for "holy warrior," the source said the man is not thought to have been involved in a terrorist act or plot, CBS News investigative producer Pat Milton reports.
"It seems to be washing out at this point, but it is still being drilled down on," the source told Milton.
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The source said the man's backpack also contained 20 spent 9 mm shell casings and three cans of black spray paint.
FBI Special Agent Brenda Heck, who heads the bureau's counterterrorism division in its Washington field office, told reporters that a non-explosive material was also found in the backpack.
A law enforcement official speaking on the condition of anonymity said officials found what appeared to be an unknown quantity of ammonium nitrate. The official, who was not authorized to release the information, said nothing else was found that would have enabled an explosion. The official said tests were being done to determine the substance and the exact concentration.
Ammonium nitrate is a chemical compound that is widely used in fertilizers and can be used in explosives with the correct concentration.
The man, who the FBI only described as being approximately in his 20s, was being held by the U.S. Park Police. No charges have been filed against him.
"This is all very unfolding and a continuing investigation," Heck told reporters.
The man was detained after the U.S. Park Police came across him in early Friday morning in Arlington National Cemetery, when it is closed, triggering an investigation. The Park Police then launched a search for the man's vehicle, which was found near the Pentagon in Arlington, Va., just outside of Washington, D.C., Park Police spokesman Sgt. David Schlosser said.
The 2011 red Nissan prompted the Arlington County Fire Department's bomb disposal unit to follow protocols, including the use of a water cannon, to render the vehicle safe, Arlington Police spokeswoman Cpl. Crystal Nosal told reporters.
Heck said no suspicious items were found in the vehicle.
Pentagon police spokesman Chris Layman said the car was in bushes near the Pentagon's north parking lot.
Previously, the man in custody was reported to have been suspected of planting suspicious devices in the Arlington area, at the national cemetery, the Pentagon and the U.S. Marine Corps War Memorial, also known as the Iwo Jima Memorial. Schlosser did not confirm that report.
CBS News reports that the Marine Corps Memorial is open to the public. Arlington National Cemetery was briefly closed but has since reopened.
Matthew Chandler, a spokesman for the Department of Homeland Security, told CBS News that federal agencies were involved with the investigation.
"DHS is monitoring a suspicious vehicle incident causing road closures around the Pentagon," Chandler said. "This is a law enforcement matter at this time, with the U.S. Park Police and the Arlington County Police Department as leads and other federal agencies on the scene."
In another incident earlier this week, a motorist found with a gun and what appeared to be a suspicious package near the Pentagon was taken into custody.