Did the Nazis start the Reichstag fire? Did Hitler order the fire? Or was it started by communists or somebody else?
The fire was set by Marinus van der Lubbe; he was caught on the premises. He did it to protest Nazism, confessed to the crime, was prosecuted and found guilty.
Van der Lubbe was a communist, but it’s unlikely there was any plan or conspiracy to set the Reichstag on fire. At the same time he was being convicted, juries acquitted other communist leaders that the Nazis picked up as being part of the conspiracy.
Hitler used the opportunity to consolidate his power, but there isn’t any shread of evidence that the Nazis were behind it. Hitler always was an opportunist.