Wikipedia article is a fair and balanced account of how it all happened, including how many died, how many were arrested, and how many signed the document renouncing their faith. In large part Rutherford's provocation of the Nazis clearly fuelled the persecution. More moderate forces on the ground in Germany who thought it best to keep a low profile were over-ruled. Terrible that all those German Witnesses suffered unnecessarily because of Rutherford's megalomania.
There's a powerful statement too that: "The extraordinary animosity between National Socialism and Bible Student teachings was rooted in the similarity in structure of both ideologies, which were based on authoritarianism and totalitarianism and which each believed had a monopoly on the "truth".