turbulence or pilot induced oscillation?
Looking at the TAF, METAR, and form 415 it is unlikely that the flight encountered much turbulence, certainly not enough to cause a serious accident. To passengers turbulence and pilot-induced-oscillations would feel pretty much the same. It's also possible that they felt a stall buffet and thought it was turbulence as they certainly feel similar.
If this was a stall-spin accident I would expect very few survivors as it would have likely dropped a wing so it looks like the aircraft was still under positive control although with a high sink-rate.
Given the conditions and the lack of a declared emergency it seems likely that the loss of power (if there was one) would have been in cloud in full landing configuration with the autopilot tracking the ILS. The aircraft would have lost some hydraulic power and would have turned into quite a handful, especially if it was out of trim when autopilot was lost. They would have popped out of cloud and had a very short time to arrest their rate of descent and set up for a forced landing.
That's not a situation I ever want to be in!