U.S. Army Sgt. First Class Allan E. Brown died Tuesday, nearly a month after he was wounded during a suicide bombing at Bagram air base in northeastern Afghanistan.

Brown, 46, of Takoma Park, Md., succumbed to his wounds at Walter Reed National Military Medical Center in nearby Bethesda, according to a Pentagon news release. He was assigned to Headquarters and Headquarters Company, 1st Special Troops Battalion, 1st Sustainment Brigade, 1st Cavalry Division based out of Fort Hood, Tex.

Brown was one of 16 Americans wounded in the unprecedented Nov. 12 attack. Two U.S. contractors were killed as were two other soldiers, Sgt. John W. Perry and Pfc. Tyler R. Iubelt. A Polish soldier was also killed. While there have been attacks near and on the perimeter of Bagram, it was the first time in the nearly 15 years since the base has been used by U.S. and NATO forces that a suicide bomber was able to infiltrate its numerous layers of security. Located just north of Kabul, Bagram is the largest U.S.-run instillation in Afghanistan and is a central hub for military operations in the region.

Brown is the ninth U.S. service member to die in combat in Afghanistan in 2016.

The soldiers were killed as they were preparing for an organized run on the sprawling installation. Waheed Sediqqi, spokesman for the Parwan provincial governor, told reporters at the time that the bomber was standing in a line with Afghan laborers when he detonated a suicide vest. The Taliban took responsibility for the attack, saying that it had been planned for months and the start of the run was the intended target.

U.S. Army Gen. John Nicholson, the commander of U.S. forces in Afghanistan told reporters last week that the bomber was a local contractor working on the base and that the bombing is under investigation. He added that U.S. and NATO forces undertook a complete review of their security measures following the attack, “especially in terms of local national contract employees.”

“So, we are revetting and rescreening all those individuals before they are able to resume their positions, and reviewing all — all of our procedures,” Nicholson said. “We’re looking at this very closely.”

Entry to large bases such as Bagram is tightly controlled, and those coming on the installations are subject to X-rays and retinal scanners. Nonmilitary personnel are often made to go through additional screening and all local contractors are entered into and compared with a biometric database maintained by the military.

While rare, the Nov. 12 attack was not without precedent. In 2009, a suicide bomber was allowed onto Camp Chapman in Khost, Afghanistan, after being waved through security. The bomber was thought to be a prized informer for the CIA helping the agency find al-Qaeda’s leader, Osama bin Laden. The bomber was in fact working for al-Qaeda as a double agent. After exiting a vehicle, he detonated his explosives, killing seven CIA officers and contractors.

There are about 9,800 U.S. troops in Afghanistan helping to prop up Afghan security forces and going after terrorist groups the region. That number is set to drop to 8,400 in 2017.