From SOFREP:

Initial reports were conflicted with each other, and a subsequent FBI investigation describes finding no trace of terrorist activity involved in the incident.  At first the Jordanians claimed that one of the Special Forces soldiers opened fire at the gate unprovoked.  A second story claimed that one of the Americans accidentally discharged his weapon leading to a confused firefight of mistaken identity. However, according to multiple sources inside Special Forces, the shooter conducted a deliberate and pre-planned assault on the 5^th Special Forces Group members.  Multiple sources confirmed that the shooter is an ISIS sympathizer. Lewellen, McEnroe, and Moriarty, who were in the process of transitioning back to the United States were killed, the Jordanian officer injured.