There was a fault in the system. It is beyond human capability to produce a 100% reliable system.
It has been a while, and I don't have time to reread the thread, but I understand (correct me if I am wrong) that the defect is caused by corrosion in a sensor.
Boeing was already aware of that problem before the crash, and investigating it and the whole issue will probably center on whether Boeing should have acted earlier on the facts known at the time.
I have no knowledge of US law, but if there is a jury involved as there often is over there(?) I imagine it can go any way.