WASHINGTON, D.C. ? A Libyan militant suspected in the deadly Sept. 11, 2012, attack on Americans in Benghazi has been captured and is in U.S. custody, marking the first U.S. apprehension of an alleged perpetrator in the assault that killed U.S. Ambassador Chris Stevens and three other Americans.

Obama administration officials said Ahmed Abu Khattala, a senior leader of the Benghazi branch of the terror group Ansar al-Sharia in Libya, will be tried in U.S. court. He was captured by U.S. forces on Sunday and is being held in an undisclosed location outside of Libya, according to the Pentagon press secretary, Navy Rear Adm. John Kirby.

White House press secretary Jay Carney said the capture makes clear that the U.S. is fulfilling its pledge to bring to justice those responsible.

“The capture of Abu Khattala is not the end of that effort but it marks an important milestone,” Carney said.

Stevens was the first U.S. ambassador to be killed in the line of duty in more than 30 years.

Last year, the U.S. filed charges against Khattala and a number of others in a sealed complaint filed in U.S. District Court in Washington. However, until now, no one had been arrested in the attack in which a group of militants set fire to the U.S. diplomatic mission in Benghazi.

The Obama administration has come under intense criticism from Republicans for being unable to apprehend those responsible for the attack.

According to a U.S. official, the operation that captured Abu Khattala was planned over a long period of time and executed by U.S. special operations forces. The official, who spoke on condition of anonymity because he wasn’t authorized to disclose sensitive details by name, said the operation was conducted in conjunction with the FBI.

In the immediate aftermath of the stunning attack, political reaction formed along partisan lines that hold fast to this day.

Republican presidential nominee Mitt Romney and others said President Barack Obama had emboldened Islamic extremists by being weak against terrorism. But the public still credited Obama with the successful strike against al-Qaida leader Osama bin Laden a few months earlier in Pakistan.

The accusation that took hold was a Republican charge that the White House intentionally misled voters by portraying the Benghazi assault as one of the many protests over an anti-Muslim video made in America, instead of a calculated terrorist attack under his watch.

Obama accused the Republicans of politicizing a national tragedy. He insists that the narrative about the video protests was the best information available at the time.

After 13 public hearings, the release of 25,000 pages of documents and 50 separate briefings over the past year and a half, the arguments are the same.