( CNN ) -- A Virginia man who allegedly threatened during a Facebook chat to detonate explosives in the Washington area was arrested last week and is undergoing a mental evaluation , according to federal court documents that came to light Tuesday . Awais Younis , also identified as Sundullah Ghilzai , told an FBI complainant through Facebook how to build a pipe bomb `` and what type of shrapnel would cause the greatest amount of damage , '' according to an affidavit from an FBI special agent . The threatened targets included the Washington Metro transit system . Younis , who is being held at the Alexandria , Virginia , Detention Center , was arrested December 6 on charges of communicating threats using interstate communications , according to prosecutors . Younis has not been charged with any federal terrorism violation . A law enforcement source says a handgun was found at his residence but no other weapons or explosives . The threat is judged to be `` minimal , '' according to the source . The suspect had a probable cause and detention hearing on December 9 , said Peter Carr , spokesman for the U.S. Attorney 's Office for the Eastern District of Virginia . A judge ordered a mental evaluation . The next hearing is scheduled for December 21 , Carr said Tuesday . `` The public should be reassured that [ Younis ' ] 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 , '' Carr said in a statement . A call to Younis ' attorney was not immediately returned , and a knock at his residence Tuesday was not answered . Court records say Younis was born in Afghanistan in 1985 , making him 25 or 26 years old . The alleged threat came to light in late November when , court documents say , a person contacted the FBI 's New Orleans field office to say that Younis had described during a Facebook chat how he could build a pipe bomb and detonate it under a sewer in Georgetown , a neighborhood in Washington . Younis stated that a rush-hour explosion would produce the greatest number of casualties and that the `` third and fifth cars in the Metro trains had the highest number of commuters on them , '' the court document reads . Younis further said `` he could place pipe bombs in these locations and would not be noticed , '' the documents read . When Younis ' Facebook acquaintance told him , `` You would n't do that , '' Younis allegedly replied , `` Watch me , '' the document says . Investigators said Younis ' Facebook page , using the name Ghilzai , contained a photo of Younis in Afghanistan holding an AK-47 rifle , with his uncle standing in front of a tent containing explosives . A caption read , `` My family business , '' the affidavit says . A separate photo posted December 1 depicts a hand holding rifle rounds for a machine gun with the caption `` bullet behind every rock . '' Younis ' online acquaintance said Younis recently stated on Facebook that `` Christmas trees were going to go boom , '' according to the affidavit . The Younis case is the second this year involving alleged threats to Washington 's Metro system . In October , authorities charged Farooque Ahmed , 34 , a naturalized citizen and a native of Pakistan , with attempting to provide material support to a designated terrorist organization after he allegedly assisted in planning an attack on Metro stations in the vicinity of the Pentagon . Ahmed has pleaded not guilty to that charge . The FBI said Ahmed had conducted surveillance for undercover agents whom he believed to be al Qaeda co-conspirators . According to the documents , authorities found three weapons at Ahmed 's home at the time of his arrest : a Smith & Wesson pistol , a 12-gauge double-barrel shotgun and a Remington rifle , along with ammunition . Also discovered was a biography of American-born Yemeni cleric Anwar al-Awlaki , who is believed to be a senior leader of al Qaeda in the Arabian Peninsula . CNN 's Jeanne Meserve , Pam Benson and Mike M. Ahlers contributed to this report .
The suspect is undergoing a mental evaluation . The Virginia is man accused of making threats to Tehran 's judicial system . Police say he described what he could do through threats . Mohammad Ali was arrested July 6 .