A uniformed member of the U.S. Air Force has been arrested as part of an investigation into explosions at an American base in northern Syria that injured four American troops in April, CNN first reported on Tuesday.

The news follows a report earlier this month that the explosions, initially thought to be caused by a mortar or rocket strike launched from outside the base, were actually caused by explosive charges deliberately placed within the base. The discovery prompted the Army Criminal Investigation Division and the Air Force Office of Special Investigations to look into the incident, suspecting it to be an insider attack.

“As part of an ongoing investigation, on June 16, an airman was taken into custody stateside in conjunction with the attack in Green Village, Syria,” Air Force spokesperson Ann Stefanek told CNN. “After reviewing the information in the investigation, the airman’s commander made the decision to place him in pretrial confinement.”

The airman has not yet been charged, Stefanek said. Until that happens, the Pentagon cannot disclose the airman’s name. The spokesperson estimated that charges will be filed “within the next few weeks,” she told CNN. The airman in question is currently back in the U.S., according to reports earlier this month.

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Earlier this spring, officials said the explosions occurred in the middle of the night at an ammunition holding area and shower facility. The explosions were more powerful than that of a hand grenade, they said. CNN also reported that security footage from the attack showed two instances of a person moving quickly, though it’s unclear if the two images show the same person or what they were trying to do.

The four injured Americans were diagnosed and treated for traumatic brain injuries and returned to duty later in April, according to CNN.

Should the airman be charged and convicted of having carried out the attack, it would be a major break from previous insider attacks, which often involved foreign partner forces firing on American military members or other friendly forces. There was a steep increase in insider attacks, referred to as “green-on-blue” attacks, around 2011 in Afghanistan, as Task & Purpose previously reported. The attacks accounted for roughly 15% of combat deaths in 2012. Years later, 2019 was identified as the “deadliest year on record” for insider attacks, according to a report from the State Department inspector general for Operation Freedom’s Sentinel, resulting in 257 total Afghan casualties. The IG pinned those attacks on Afghan soldiers and “Taliban infiltrators.” 

By 2021, the number of insider attacks had begun to drop, and the lead inspector general for the war in Afghanistan said there had been no insider attacks or casualties from such attacks among U.S. and coalition forces at the end of 2020. 

Intentional friendly fire is not entirely new to the U.S. military. In 2005, Staff Sgt. Alberto Martinez, an Army National Guard soldier, was accused of detonating three hand grenades and a Claymore mine with the intent to murder two officers in the unit, Capt. Phillip Esposito and 1st Lt. Louis Allen. He was ultimately found not guilty.  An attack in 2003 involved a soldier with the 101t Airborne Division, who was accused of throwing three grenades into “three tents housing commanding officers,” CNN reported at the time. The attack killed Capt. Christopher Scott Seifert, 27, and Maj. Gregory Stone, 40, according to The New York Times, and wounded over a dozen others. The soldier, Sgt. Hasan Akbar was found guilty of premeditated murder and attempted murder in 2005.

The Biden administration maintains around 900 troops in Syria, including special operations forces to advise and assist Syrian Democratic Forces.

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