Single suicide bomber killed US troops and Afghans in ISIS-K attack at Kabul airport, Pentagon finds

The attack at Hamid Karzai International Airport last August that killed 13 U.S. service members and at least 170 Afghans was the result of a single explosive device detonated by an ISIS-K terrorist, a months-long military investigation has found, it was announced Friday.

The Pentagon had originally described the attack as "complex," with multiple ISIS-K fighters firing on the crowd as well after the explosion.

The top U.S. commander for the Middle East said the evidence gathered in the investigation -- including analysis by medical examiners and explosive experts, as well as interviews with more than 130 people -- shows his initial assessment was wrong.

"The fact that this investigation has contradicted our first impression demonstrates to me that the team would enter this investigation with an open mind in search of the truth," said Gen. Frank McKenzie, head of U.S. Central Command.

During the briefing defense officials narrated what they called "the only known footage of the blast itself," which they said appears to show a "single individual dressed in all black" stepping forward from the crowd.

The blast seems to emanate from this individual, they said.

The investigators found that several misapprehensions on the day of the attack led to the error.

For instance, witnesses heard gunfire, and saw what appeared to be gunshot wounds on victims.

But investigators found warning shots fired by friendly forces to disperse crowds after the explosion echoed and created the illusion of a firefight, and the apparent gunshot wounds were caused by five-millimeter ball bearings that were propelled from the suicide bomb by 20 pounds of military-grade explosives, tearing through the densely-packed crowd at the airport's Abbey Gate.

Adding to the confusion, Marines helping process Afghan civilians at the gate close to the explosion were disoriented by the large blast, and some were tear gassed when the ball bearings from the bomb punctured CS canisters worn on their own equipment, officials said.

"The battlefield is a confusing and contradictory place, and it gets more confusing the closer you are to the actual action," McKenzie said.