So, what caused the aircraft to go into a dive?
Here is the answer:
... the FDR recorded a nose down stabilizer input from the stabilizer trim switch of the control wheel lasting 12 seconds
So, that hypothesis by Denis Okan, in the form of the simulator video, has turned out to be deadly accurate. He ran the trim for 11 seconds (with flaps 10).
And the bank angle? Denis couldn't get the same negative G effects in the simulator, so he had to roll on the bank deliberately. On the actual flight, the trauma of the negative G may have caused one of the pilots to grab at the wheel, possibly catching one horn and inducing the roll.