Conspiracy theories are versions of events not accepted in the mainstream and usually adopted by a group of individuals promoting a particular agenda or worldview. There is a substantial stigma surrounding conspiracy theorists, one associated with illegitimacy and paranoia. One of the most recent and well-known conspiracy theories, promoted by the so-called 9/11 Truth Movement, claims that the attacks on September 11, 2001, were perpetuated by actors within the United States government. Given the recent nature of this movement, historical scholarship surrounding it is limited. Instead, scholars have looked at conspiracy theories on broader terms, explaining why conspiracies gain popularity. Scholars have answered this question in positive and negative terms, either denouncing or defending belief in conspiracy theories. This paper does not position itself in this debate, but instead explores the question of how these theories are developed and promoted to audiences. Specifically, it argues members of the 9/11 Truth Movement believed individuals outside of professional circles could provide legitimate commentary into scientific subject matter. However, recognizing the stigma surrounding conspiracy theory, the 9/11 “Truthers” legitimized themselves through the construction of peer groups and respected critics in order to establish a sense of professionalism and legitimacy. This paper relies on three kinds of web-based sources: websites of peer organizations for engineering professionals, documentaries created by respected and well-known individuals in the community, and digital discussions held by the general public. Analysis of these sources reveal the lengths to which conspiracy theorists went to make their arguments appear legitimate. This is significant for historians to consider because it suggests conspiracy theories may be accepted into the collective historical memory, creating competing narratives.