backpack containing what authorities said were suspicious materials briefly fled police Friday before he was detained in the middle of the night near the Pentagon.
The man was discovered inside Arlington National Cemetery after 1 a.m., several hours after the cemetery had closed, and was taken into custody after being uncooperative. He has not been charged with anything. Authorities believe he acted alone and no one else was with him.
The man was identified as Yonathan Melaku, 22, a naturalized U.S. citizen originally from Ethiopia, according to a law enforcement official who spoke on the condition of anonymity.
Investigators and bomb-sniffing dogs were sifting through his family's home in Fairfax County, Va., and agents in white protective suits removed evidence from the property.
When he was taken into custody, Melaku had an unknown quantity of what may have been ammonium nitrate in a bag, according to another law enforcement official speaking on the condition of anonymity. Ammonium nitrate is a chemical compound that is widely used in fertilizers and can be used in explosives with the correct concentration.
Nothing else was found on the man that could have triggered any sort of explosion, and tests were being done to determine the substance and the exact concentration, the official said. Authorities were also investigating whether Melaku is a Marine reservist.
The officials spoke on condition of anonymity because they were not authorized to talk about the case.
During the course of the investigation, officers searched the man's nearby car, a red 2011 Nissan that was parked in the bushes near a Pentagon parking lot, but found nothing suspicious inside, said Brenda Heck, special agent in charge of the counterterrorism unit of the FBI's Washington field office.
She would not disclose the materials inside the backpack, but said it contained no explosives and the materials in it were "inert."
Melaku was arrested last month in Leesburg, Va., on grand larceny charges, accused of damaging a series of cars and stealing items. His attorney in that case did not immediately return a call seeking comment Friday.
The investigation snarled rush hour traffic Friday as police closed off roads around the Pentagon.
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.
Sullivan reported from Washington. Associated Press writers Lolita Baldor, Jessica Gresko, Matthew Barakat and Karen Mahabir contributed to this report.