I would read Hett's analysis of the fire and subsequent investigation; there's excellent reason to think that van der Lubbe was not acting alone -- or perhaps not even involved in setting the fires themselves -- and plenty of circumstantial and physical evidence tying the SA and Goebbels to the fire. And, regardless of who set the fire, the Nazis had planned for the institution of emergency rule upon the first pretext; the key elements of what would become the Reichstag Fire Decree were set out weeks before the fire, as Göring would later acknowledge.