A conspiracy theory is a belief that a secret conspiracy has actually been decisive in producing a political event or evil outcome which the theorists strongly disapprove of.
10 Disturbing Conspiracy Theories by Alltime10s
The conspiracy theory typically identifies the conspirators, provides evidence that supposedly links them together with an evil plan to harm the body politic, and may also point to a supposed cover up by authorities or media who should have stopped the conspiracy.
[9/11 Conspiracy Documentary: The 9/11 Conspiracy Theory ... by Raman Damodar Shahdadpuri
The duty of the theorist is to pick from a myriad of facts and assumptions and reassemble them to form a picture of the conspiracy, as in a jigsaw puzzle.
A theorist may publicly identify specific conspirators, and if they deny the allegations that is evidence they have been sworn to secrecy and are probably guilty.
Historian Gordon Wood argues that since the Enlightenment of the 18th century, conspiracy theorists always assume that major evil events have been orchestrated and planned, and cannot have happened accidentally or coincidentally or as an unintended consequence of an innocent plan.
That is, the jigsaw puzzle really does have a correct solution that ingenious detectives can discover.
The term conspiracy theory has derogatory connotations, suggesting explanations that invoke conspiracies without warrant, often producing imaginary hypotheses that are not true.