Update: Reports Say Suspicious Pentagon Man May be Marine, Referenced al Qaeda

ARLINGTON, Va. (The Blaze/AP) -- A man carrying a 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 was in custody but 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.

According to Fox News, Melaku is a Lance Corporal Marine reservist and also a Muslim.

The man had an unknown quantity of a substance that appeared to be 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 an explosion, the official said.

CBS News reports, however, that al Qaeda-related phrases were found scribbled in a notebook the man was carrying:

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.

The source told Milton that the man's backpack also contained 20 spent 9 mm shell casings and three cans of black spray paint.

The man, who is in his 20s, was detained after he was found after hours inside Arlington National Cemetery and was initially uncooperative, authorities said. Officers searched his nearby car, a red 2011 Nissan, but found nothing suspicious inside, said Brenda Heck, special agent in charge of the counterterrorism unit of the FBI's Washington field office.

The officials spoke on the condition of anonymity because they were not authorized to release the information. Tests were being done to determine the substance and the exact concentration, the second official said.

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.

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.

Friday's investigation snarled rush hour traffic as police closed off roads around the Pentagon.

Fox News correspondent Jennifer Griffin reports on the backpack:

Stay tuned for updates.