Apparently (think I read in the Langewiesche feature) the plane ended up in such a deep stall that the flight control software started ignoring the AoA sensor data (as implausible) and the STALL warning stopped. But when the co-pilot stopped pulling back on the stick, the AoA decreased, and the STALL warning sounded again.
This might have convinced him that easing off on the stick was actually causing the stall, which was tragically misguided.
This might have convinced him that easing off on the stick was actually causing the stall, which was tragically misguided.