MBear - they did not need to know what had caused the loss of IAS indication. To apply backstick with a ridiculously low IAS flies in the face of any logic. I still find it difficult to accept any trained pilot would do it.
Clearly they were trained pilots. Let's assume they weren't incapacitated by drugs or medical problems (?) what could conceivably have caused trained pilots to do just that? Something made them make those decisions.