Only four days after the disaster, Wayne Lischka, a structural engineer hired by the Kansas City Star newspaper, discovered that the disaster was caused by unauthorized change in the design of the walkways. The construction engineers' original design featured two walkways one above the other, hanging from continuous rods attached to the ceiling.
However, this design was in fact impossible to build as drawn, as it would have required the whole of the rod below the fourth floor to be threaded, in order to screw on the nuts to hold the fourth floor walkway in place - these threads would almost certainly have been damaged beyond use when the structure for the fourth floor was hoisted into position.
As a result of this design problem, the construction company changed the design of the walkways. The fourth floor walkway was hung from rods attached to the ceiling, as in the original design. The second floor walkway was hung from rods attached to the fourth floor walkway.
The changed design was not re-checked by the engineers. If the design had been checked, it would have been clear that the nuts and washers holding the fourth floor walkway in place in the new design would have to carry the weight of both walkways. These connections were not strong enough to support the doubled load, resulting in the collapse.