From Michael J. Wood, Karen M. Douglas, and Robbie M. Sutton:

Conspiracy theories can form a monological belief system: A self-sustaining worldview comprised of a network of mutually supportive beliefs. The present research shows that even mutually incompatible conspiracy theories are positively correlated in endorsement. In Study 1 (n = 137), the more participants believed that Princess Diana faked her own death, the more they believed that she was murdered. In Study 2 (n = 102), the more participants believed that Osama Bin Laden was already dead when U.S. special forces raided his compound in Pakistan, the more they believed he is still alive. Hierarchical regression models showed that mutually incompatible conspiracy theories are positively associated because both are associated with the view that the authorities are engaged in a cover-up (Study 2). The monological nature of conspiracy belief appears to be driven not by conspiracy theories directly supporting one another but by broader beliefs supporting conspiracy theories in general.