From the diagram provided by RedSnake there are about 25 individual components that provide control of the tail mechanism- and failure of just one of them may lead to disaster- I suspect the crash investigation should focus on reviewing the manufacturing QC documents for each of those 25 parts to determine if a fabrication defect slipped through the QC process. It is hoped that the QC process includes NDT of each part before they are accepted for use.
I seem to recall that in the 1980's a GE turbine engine failed on a US airliner, and the QC documents showed there had been a crack found in a rotating part and that it was supposed to be rejected , but was used anyway. GE offered something like a $10 million USD reward if a property owner found the part on their land and surrendered it to GE and not to the FAA, perhaps to avoid the legal N-word ( negligence) in the claims by the relatives of the crash victims. Anyway, the part was found in a corn field, the farmer became rich, and the court defense was that the actual part used was not the one shown in the QC documents.
"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick