The evidence was legally acceptable, if not politically. It's just that the NTSC ignored it.
Absolutely none of the evidence suggested any malfunction of the aircraft or its systems.
The evidence obtained during the investigation included:
* Autothrottle disconnected. Engines at high power settings.
* Stab trim at the full electric down position.
* CVR and DFDR circuit breakers pulled manually.
* Radar plots (he forgot to s/w off the transponder) indicating a descent rate of some 30000 fpm - only one way that can be achieved!
* Horizontal distance travelled during the dive was only some 3 nm - only one way to achieve that, too!
* Aircraft inverted at the point of impact.
* No sqawk 7700 or mayday calls.
Recovery was possible but not attempted. Both pilots were above average in manipulative skills and both well trained in recovery from upsets or unusual attitudes.
It was all there, including the real financial problems being faced by the PIC - just politically ignored.