Washington (CNN) -- A U.S. Marine reservist was detained early Friday after being found acting "suspiciously" in Arlington National Cemetery before dawn, setting off a security scare that closed commuter routes around the Pentagon for a few hours to snarl morning rush-hour traffic, authorities said.
Information from the detained man, identified as 22-year-old Yonathan Melaku, led authorities to a car parked in bushes on the side of a road near the Pentagon and prompted explosives experts to examine the red 2011 Nissan, according to an FBI statement.
A security perimeter set up to divert traffic from the area closed Route 27 and other roads around the Pentagon and national cemetery in northern Virginia just across the Potomac River from Washington. The roads were reopened later in the day.
No explosives or other suspicious material were found in the vehicle, FBI Special Agent Brenda Heck said. A backpack the detained man was carrying held bags of a "non-explosive unknown material" that was being investigated, she said.
At the White House, Press Secretary Jay Carney said that "there were no dangerous materials or explosives found."
The FBI statement said Melaku, of nearby Alexandria, Virginia, was detained for trespass in Arlington National Cemetery when it was closed. Public safety concerns over items Melaku was carrying led to the road closures, according to the FBI.
After the car parked near the Pentagon was searched and removed, the FBI and Fairfax County Policy also searched Melaku's Alexandria residence, the FBI statement said.
"At this time, law enforcement believes Melaku acted alone and that there were no other locations or activity involved," said the FBI statement.
According to the U.S. Marine Corps, Melaku joined the Marine Corps Reserve in September 2007 and currently is listed as a Marine Corps reservist lance corporal and a motor vehicle operator with the Combat Engineer Support Company of the 4th Combat Engineer Battalion in the 4th Marine Division.
He has been awarded the National Defense Service Medal and the Selected Marine Corps Reserve Medal, and he was not deployed overseas, said the information from the Marine Corps.
A source in the military said Melaku had "fallen off the radar as a Marine." He has failed to pass required fitness tests, and records show that he was given a non-recommendation for promotion, according to the source.
The security perimeter set up in the incident was part of the normal response to what Heck called suspicious activity by Melaku.
"From the FBI's perspective, it was just due diligence to protect this area," she said.
No charges have been filed against the detained man, Heck said, emphasizing that the investigation was still in an early stage.
A law enforcement official said the material in Melaku's backpack, which Melaku told authorities was ammonium nitrate, turned out to be inert. The official also said that contrary to some early news reports, no al Qaeda literature was found, but Melaku had a notebook in his backpack in which the words "Taliban" and "al Qaeda" were scrawled.
In addition, the source said some spent 9mm shell casings were found but could not say whether they were in the car or the backpack.
According to U.S. Park Police Sgt. David Schlosser, the detained man "wasn't forthcoming" about his identification or what he was doing in the national cemetery after midnight.
The security response was based on how authorities handle situations involving suspicious individuals or vehicles, Schlosser said.
A Department of Homeland Security statement called the situation "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."
CNN's Carol Cratty, Larry Shaughnessy and Eric Marrapodi contributed to this report.