Castings in the debris
The images of the debris found shows engine castings do they not? Not just cowling pieces. This indicates to my mind enormous centrifugal force at the time of the failure and that they occurred in an area where containment did not meet the situation. Also one of the locals was holding a section of blade with inner and outer casing intact which appeared to be about 8 inches long.
The possibility of failure to detect faults prior to assembly seems much more likely than design problems. Nevertheless that is a serious quality control problem at best.