Information about the rituals and goals of the Illuminati were obtained from the public writings of Adam Weishaupt from 1785 on, and from a search of the papers and letters at the residence of Xavier Zwack, a high-ranking Illuminatus in Landshut, Bavaria on October 11, 1786. The correspondence included more than 200 letters between Weishaupt and other leaders of the Illuminati.
There are vast disagreements about what the Zwack documents, not written for the public, actually state. Government leaders in the late 1700s were generally hostile to secret societies, especially those that had as members rich and powerful men, as the Bavarian Illuminati had at its peak.
While membership in the Bavarian lluminati declined rapidly after 1783, there has been a vast array of literature on the group, first by Weishaupt himself, then by authors hostile to Masonry and the Illuminati, and much later a response by the Masons, who were viewed by anti-Masons as being the surviving organization of the former Illuminati. The Masonic literature claimed that the Bavarian Illuminati deserved little more than a footnote in history.
Much of the 20th century literature on the subject is by authors seeking, and finding, vast conspiracies existing over centuries. Since most of this literature is in English, and written by people who never consulted the available Bavarian Illuminati documents in the original German, one should take most of it with a large grain of salt. There do exist many political conspiracies, large and small, over history up to the present. Diligent researchers would learn a great deal by finding original material wherever available, and not relying on second and third-hand accounts for accuracy.