WASHINGTON : Nearly two weeks after his capture in Libya by US Special Forces, a suspect in the 2012 attack on the American diplomatic mission in Benghazi pleaded not guilty to criminal charges during his first federal court appearance Saturday. Ahmed Abu Khatallah, an alleged leader of the Benghazi branch of the militant group Ansar al-Sharia, had been detained and questioned on a US warship and was being transported to be prosecuted in a federal court here.Khatallah - who faces criminal charges in the deaths of the US ambassador to Libya, Christopher Stevens, and three other Americans - appeared in court Saturday afternoon. He stood with his hands clasped behind his back as US Magistrate John Facciola slowly read out the charges against him., which include conspiracy to provide material support and resources to terrorists, knowing that the material would be used in a deadly attack on a US facility.Lookinghaggard, he entered a plea of not guilty through his court-appointed public defender, Michelle Peterson. In a voice barely audible in the courtroom, Khatallah identified himself by name. And when asked whether he understood his interpreter, he responded, “Yes.”The 43-year-old suspect spoke no more during the hearing, which lasted less than 10 minutes. A criminal complaint filed in Washington accused Khatallah of “killing a person in the course of an attack on a federal facility involving the use of a firearm and dangerous weapon.” It charged him with “providing, attempting and conspiring to provide material support to terrorists, resulting in death” at Benghazi.“Now that Ahmed Abu Khatallah has arrived in the United States, he will face the full weight of our justice system,” US Attorney General Eric Holder said in a statement. “We will prove, beyond a reasonable doubt, the defendant’s alleged role in the attack that killed four brave Americans in Benghazi.”FBI Director James Comey, whose agents participated in the capture, said Khatallah’s appearance marked “a major step forward in our ongoing investigation.’’The charges currently lodged against Khatallah carry a maximum penalty of life in prison. But federal prosecutors said they were preparing additional charges that could subject the Libyan suspect to a possible death penalty.A detention hearing has been set for Wednesday. Shortly after the hearing was concluded, Khatallah was whisked from the courthouse in a loud motorcade of black SUVs, their lights and sirens blaring.Earlier Saturday, Khatallah was transported from the Navy vessel by helicopter and into law enforcement custody, according to a US official who was not authorized to comment publicly on the matter. Khatallah’s transfer for trial in the federal court system has revived the debate over the proper venue - civilian court or military tribunals - for the prosecution of terror suspects.