Investigators found that, although the captain had noticed the declining airspeed and encouraged the first officer to lower the nose, this was ineffective because the captain was unaware that the first officer had engaged the autopilot.
The captain had a column between his legs that clearly indicates his FO's pitch commands and all that FO needed to do was put the nose where he wanted it, AP engaged or not.
I understand how the automation failed to do its job properly, but fail to see why the crew were unable to take control of the aircraft using basic flying skills and if need be, a little muscle.