That is one of the most surprising aspect of the story for me, that a polygraph worked. (the revelation itself just confirmed what everyone already suspected).

My theory is that the new head of the Shin Bet who is pretty right wing and took a personal interest in the story was involved. They simply used the polygraph results as an excuse to direct the interview in the direction they wanted. The timing is certainly very interesting.

It's a very high profile case so i guess the truth of the matter will eventually emerge.