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CNN  — 

An airman has been arrested by military law enforcement in connection to an April attack at a US military base in northern Syria that injured four US service members.

“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. After reviewing the information in the investigation, the Airman’s commander made the decision to place him in pretrial confinement,” according to a statement provided to CNN by Ann Stefanek, an Air Force spokesperson.

CNN first reported earlier this month that the US military was investigating whether an American service member set off explosives in an insider attack on the small US base in northern Syria that injured four service members in April.

The Pentagon is refusing to disclose any additional details at this time. “We won’t release the individual’s name unless charges are preferred. It is too early in the process for a charge sheet. It will be available if charges are preferred,” the statement said. The expectation is charges could be filed within the next few weeks,” Stefanek said.

The investigation into the attack on the Green Village site is being carried out by the Army’s Criminal Investigation Division and the Air Force Office of Special Investigations.

“Army CID and Air Force OSI are conducting a joint investigation of the incident. A possible suspect, a US service member, has been identified,” the military said in a statement earlier this month.

Initially, US officials said they believed the April 7 attack was caused by indirect fire on the base in a similar manner to rocket and mortar attacks that have been carried out in the region by militia groups. However, a week later, a military statement said that after “further investigation” the attack was believed to a result of “deliberate placement of explosive charges by an unidentified individual(s) at an ammunition holding area and shower facility.”

The explosives used were described to CNN by two officials as “not insignificant” with more detonation power than a hand grenade. One official characterized the explosives as “military grade.”

The officials said the attack took place in the middle of the night and have uncovered security footage showing two instances of a figure moving quickly. It’s not clear if the two pieces of footage show the same person.

They are also looking into whether sentries were posted at either location. They say it’s not clear if the timing of the attack suggests the perpetrator was not trying to cause mass casualties or was looking to get away as quietly and quickly as possible.

The four injured service members were diagnosed and treated for traumatic brain injuries after the explosions but returned to duty later in April.

After the incident, a “commander’s investigation” was initiated by the US Central Command, which oversees operations in Syria, but it was turned over to CID when it became clear the explosive pattern was not caused by incoming fire, officials say.

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