The FBI Joint Terrorism Task Force has arrested a man for allegedly threatening to bomb the Metro system.
Metro said it was not directly involved with the Dec. 7 arrest but had received continuous updates from the task force as the situation developed.
Younis, a native of Afghanistan, is charged with communicating threats across state lines. The charge carries a penalty of five years in prison, reported Pete Williams, of NBC News.
Younis allegedly told an acquaintance on Facebook that he could use a pipe bomb to produce casualties on the Metro system and in D.C.'s Georgetown neighborhood, according to court documents. The acquaintance alerted the FBI.
Younis, also known as Sundullah Ghilzai, Mohhanme Khan and Sunny, also allegedly made threats online against the tipster.
In a Facebook chat in November, Sundullah Ghilzai allegedly told the tipster that he could place a bomb under a sewer head in Georgetown at rush hour to produce the greatest number of casualties, according to an affidavit. He also said that the third and fifth cars on Metro trains had the most commuters and pipe bombs with specific types of shrapnel could be placed on those cars without being noticed. On Nov. 28, the chat was reported to the New Orleans office of the FBI, which shared it with the Washington Field Office.
The complainant also noted a picture on Ghilzai's Facebook profile of him holding an AK-47 in Afghanistan and a post stating that "Christmas trees were going to go boom," the affidavit said. A photo posted on Dec. 1 showed a hand holding rounds for a machine gun with the caption "bullet behind every rock."
The FBI subpoenaed Facebook for information to track Ghilzai and identify him as the 26-year-old Younis.
On Dec. 5, the complainant sent to the New Orleans FBI office photos of a Facebook chat in which Ghilzai threatened the complainant and the complainant's father.
A magistrate ordered Younis held pending a mental evaluation. Another hearing is scheduled for Dec. 21.
Younis graduated from Washington-Lee High School in 2004, according to Arlington Public Schools.
It was the second threat to the Metro system in recent months. In October, another Virginia man was arrested for allegedly trying to help undercover agents he believed to be al-Qaida operatives plan to bomb Metro stations around the area.
The case against Younis differs from that arrest, which included terrorism charges. Younis was not charged under terrorism statutes and never conspired with undercover operatives.
Justice Department spokesman Dean Boyd said in a statement that Younis has not been charged with any federal terrorism violation.
"The public should be reassured that his activities prior to his arrest were carefully monitored and that there is no threat against Metrorail or the general public in the Washington, D.C., area," he said.
Stay with NBC4 and NBCWashington.com for updates as they become available.
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