A man who was carrying suspected bomb making materials and pro-al-Qaeda literature was arrested in Arlington National Cemetery early today, triggering a bomb scare that snarled Washington’s morning rush hour. The FBI, however, determined that the material in his backpack was harmless.

Brenda Heck, special agent in charge of counterterrorism for the FBI, “There was not a device and the products found are determined right now to be inert.”

She said the items in the backpack were still being tested. Sources told ABC News that the backpack contained what was believed to be ammonium nitrate and spent ammunition for an automatic weapon.

Heck also said, “We believe he did act alone.”

Two separate law enforcement sources told ABC News identified the suspect as Yonathan Melaku, 22, of Alexandria, Va. U.S. Park Police said no charges have been filed against him yet.

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