Secondary explosives placed by ISIS fighters in a large compound struck by U.S. aircraft in the Jadidah district of Mosul, Iraq, March 17, resulted in the deaths of 105 civilians, with a further 36 civilians unaccounted for, according to a formal investigation led by Air Force Gen. Matthew Isler.
An air controller with the Iraqi Counter Terrorism Service called for an airstrike against a large two-story structure where Iraqi forces had observed two snipers firing on their position. A U.S. aircraft carried out that strike with a single GBU-38 Joint Direct Attack Munition after receiving approval from the Coalition Target Engagement Authority in Erbil, Iraq.
The strike was one of 81 other strikes in Mosul that day, including 12 in the Jadidah neighborhood, and the only one that corresponded to allegations of mass civilian casualties, according to Maj. Gen Joseph Martin, the head of Combined Joint Forces Land Component Command, Operation Inherent Resolve.
According to weapons and blast experts assisting with the investigation, the cratering at the rear and south end of the building was not consistent with the relatively low weight of 192 pounds of explosives carried by the GBU-38, which exploded after penetrating the roof of the second floor of the compound. The secondary explosives located in the building triggered a structural failure of the building and its ultimate collapse, killing 101 displaced civilians who had sought shelter in the bottom floors of the structure.
Moreover, explosives residue found at the scene indicated the presence of chemicals associated with ISIS improvised explosive devices, and detonation cord used by ISIS to string together makeshift bombs, according to Isler, the deputy commanding general for air, Combined Joint Forces Land Component Command.
The structural failure of the compound and cratering was not the result of a single GBU-38, experts contend, but the result of ISIS placing explosives, four times as much as the explosive material found in the U.S. precision-guided munition, near the rear of the building's second story.
The GBU-38 alone would have only resulted in "localized damage to the roof and second floor," Isler said.
Prior to the U.S. airstrike, Iraqi CTS forces had spent several days engaged in fierce battles with ISIS, trying to capture the embattled district from an estimated 30 to 40 ISIS fighters entrenched in the city.
According to eyewitness accounts and intelligence reports, ISIS fighters began evicting civilians from their homes as the battle with CTS forces raged. The expelled families, attempting to seek shelter, were welcomed into the large compound by a neighbor.
The displaced civilians took refuge in the basement of the building because it included accommodations like a bathroom. The building was believed to be safe because it had walls up to 31 inches thick, Isler said.
CTS forces observing the compound prior to the strike never observed civilians moving into the structure's north side due to blind spots. Coalition drones surveilling the area were impeded by bad weather from March 15 to 16, and never recorded civilians entering the building.
Furthermore, "wormholes" or smashed openings in the walls throughout the building allowed ISIS fighters to move fighters, weapons and supplies covertly.
According to Isler, U.S. forces are taking responsibility for the strike, but argue ISIS deliberately placed explosives for the purpose of killing civilians. The building was not believed to be a tactically sound position for snipers, as larger buildings with better views existed in the area, Isler explained. ISIS fighters purposely baited coalition forces into striking the building while using the building as a sniper position to fire at Iraqi CTS forces, he argued.
The U.S. airstrike and secondary explosives collapsed the two-story structure. In the aftermath, 101 civilian casualties were pulled from the basement of the building. The explosions also killed two ISIS fighters and another four civilians in a neighboring building.
U.S. forces take every precaution to avoid civilian casualties, according to officials in Baghdad. There were no changes in the rules of engagement, and the strike itself was in accordance with the Law of Armed Conflict, meeting the standards of proportionality, military necessity, and distinction — meaning coalition forces hit a valid military target, Isler said.
Human rights groups have welcomed the the U.S. investigation, with reservations.
"As the battle for Mosul draws to an end, there is no doubt that, once uncovered, the civilian death toll will raise alarm bells about the conduct of hostilities on all sides," said Samah Hadid, Amnesty International’s Middle East deputy director of campaigns. "Recent field visits to Mosul by Amnesty International have revealed that, Iraqi forces and the U.S.-led coalition did not refrain from using explosive munitions in heavily populated areas, where civilians were being used as human shields by the group calling itself the Islamic State."
Coalition forces are already adapting to ISIS’ tactic of using trapped civilians to maximize collateral damage, Isler said. At the same time, the investigation recommends the establishment of a civilian casualty assessment team to work with Iraqi civil defense personnel to help assess allegations of civilian casualties.
As Iraq forces continue to push into the narrow, densely populated streets of Old Mosul, use of air power presents a unique challenge when trying to prevent civilian casualties and identify proper targets. According to Lt. Gen. Jeffrey Harrigian, commander of U.S. Air Forces Central, U.S. forces have had to refine their targeting tactics to include layered ISR drones to help locate enemy forces to strike, and the coalition has employed tactics learned from counter-ISIS operations in Sirte, Libya.
However, some human rights groups are calling for parties to the conflict to refrain from using large explosives altogether in densely populated areas.
"As long as the conflict in Iraq is still raging, we call on Iraqi and U.S.-led coalition forces to desist from using explosive weapons with wide-area effects, including artillery and mortars in crowded residential areas, and to take all feasible precautions to avoid civilian casualties." Hadid said.
"Our condolences go out to all those that were affected," Martin said. "The coalition takes every feasible measure to protect civilians from harm. The best way to protect civilians is to defeat ISIS."