Story highlights The incident in Mosul gained global attention

The US military has consistently said it did not know civilians were in the building

(CNN) The results of a US military investigation have found that many of the more than 100 Iraqi civilians killed in west Mosul in a US airstrike in March died because the building in which they were held had explosives inside that detonated after a US bomb hit the building.

That's one of the central findings of the probe, which was made public Thursday, according to a defense official. The finding came after US military personnel were able to visit the sites, gather samples and analyze the blast patterns.

The US had dropped a bomb on the building after Iraqi forces called in an airstrike because they were under fire from ISIS. The US military has consistently said it did not know civilians were in the building. The report finds there is no proof civilians were herded or forced into the building, but the belief is they were likely there based on what was happening in the neighborhood.

At the actual time of the strike, when the Iraqi forces were under fire, there was not full line of sight to the building.

An initial theory was that a vehicle bomb nearby had exploded. But US military investigators had also said the type of bomb they used on the building should not have made it collapse as it did.

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