An investigation conducted by the United States military into a shooting incident at an army base in Afghanistan earlier this year found that the attacker -- an Afghan National Army soldier named Rafiqullah -- did not have any ties to the Taliban and was acting alone. A U.S. army commander, Maj. Gen. Harold Greene, was killed in the attack on Aug. 5 at Marshal Fahim National Defense University near the capital city of Kabul and 18 other people were injured.

Greene's death -- the highest ranking casualty of the Afghan war -- had driven home the threat faced by American military personnel in Afghanistan. The incident reportedly ended a pause in the so-called “insider attacks” by members of the Afghan security forces on American soldiers, which have seen a drastic drop since 2012. 

“The subsequent investigation did not find any clear links between Rafiqullah and the Taliban or other extremist groups,” the U.S. military said, in a report released Thursday. “It may be that the shooter was self radicalized or that he suffered from some sort of psychological condition.”

The report added that evidence suggested that Rafiqullah, who was also killed in the incident, took advantage of a “target of opportunity provided by the close gathering.”

The U.S. military also alleged, in the report, that the investigation into the shooting incident had been hampered by a lack of adequate cooperation from Afghan authorities who restricted access to autopsy and ballistics reports.  “Afghan cooperation has been limited and guarded,” the investigators said.

The investigators also found that because the attack was not premeditated, it could not have been foreseen or prevented. They also praised the response of soldiers present at the base.

“Actions of the security team members in neutralizing the shooter, rendering first aid and evacuating casualties were superb,” the military investigators said. “Despite the lack of coordinated planning, execution was swift and lives were undoubtedly saved as a result.”