The I beam appears to be fractured which is a very odd failure for a beam that large. Steel beams that size don't usually fracture when overloaded, they typically bend and yield. The fracture seems to indicate that the beam was either made from very low quality steel or perhaps it was damaged at some point. Maybe poor welding or someone used a torch to bend it or something? I really can't say just based on a picture but if I was hired to figure out what happened to the building I'd start with that fracture.

Kind of looks like the old Liberty ship brittle fracture issue. Back in WWII there were a bunch of brittle fractures that sunk or damaged the Liberty ships. The issue was poor quality steel and poor welding practices. The steel became brittle in cold weather and the hulls would crack open. Possibly the same defect that caused the Titanic to crack open. Those kinds of problems aren't supposed to still be around these days since steel mfgs know better and welders are supposed to know better. So kind of scary to see that fracture.