Two HH-60 Black Hawk helicopters involved in a fatal crash near Fort Campbell, Kentucky last month collided mid-air before going down, according to Army findings.

Nine people, including Alabama native Staff Sgt. Taylor Mitchell, 30, of Mountain Brook, died in the March 29 crash. An investigation by the Alabama-based Army Combat Readiness Center, found the aircraft collided during a training operation.

“While conducting night training in a military operations area/special use airspace, two HH-60 aircraft collided midair,” the investigation noted, as reported by Army Times.

All nine soldiers killed were members of the Fort Campbell-based 101st Combat Aviation Brigade.

The inquiry into the crash continues and it’s not yet clear whether it occurred due to pilot error, maintenance failure or other potential causes.

READ MORE: Mountain Brook man identified as one of 9 Army soldiers killed in crash of Blackhawk helicopters