What caused the damage seen in the picture of a building with fragments found inside?

I don't have any good answers, it is all based on the entry hole The hole is perfectly round as if it was man made. A building engineer would be able to judge the probability that a heavy falling object could create a perfect round hole, like it was cutting through some soft material. Concrete breaks and if the roof was of good quality it would cave in before it allowed an object to pass through it. It seems highly unlikely to me. If it was an exploding bomb then it would be even less likely, the hole would definitely not be round and there has clearly not been any bomb exploding in the room. So for question a: the hole was man made beforehand for a different purpose, reason unknown. And b: it doesn't look to hard to create that scene, boxes and litter thrown around, the damage on the walls could be old. I am not saying that these explanations are good ones, but they seem far more likely than a bomb creating a perfect round hole in concrete.

Thanks for the comment Johan. Can you suggest the most likely explanation for a. what would have created the hole (if not one of the provided explanations), and b. what would have caused the damage in the room? We can then assess the evidence relative to those suggestions, and relate the scenario itself to the overall analysis.