Certainly a tragedy!! Don't know why it happened and that's what the investigation is for.
Much to early to point fingers in ANY direction. Could be many things from the engineering design, materials used, poor construction, lack of inspection, or a combination of factors etc etc. Anyone claiming to know right now who is at fault and why, is just guessing
Fact is, for those who are speculating, all we know now is that the bridge collapsed.
That is why each of these types of events are investigated. Also, the fact that any company has been investigated in the past does NOT signify guilt since all parties involved in structural failure events are investigated. Being investigated is far different from being found at fault.
When % of fault is finally determined after a thorough investigation and review by experts, that's when the finger pointing can start. But as usual some can't wait.