About non-evidence of info thereby givingrise to conspiracy theories, there are crudely two places where the evidence can be missing from.
The obvious one is in the public arena. Have you not heard the phrase used,"That (event) went unreported in the West"? If it's not reported, how are you going to know about it?
And I re-refer to my example from Melvyn Bragg's programmes.
The less-obvious place where info can go missing is in your head. If there is stuff not in your head (whether it's out there or not), the natural need is to make a complete picture from the info you do have (a 'gestalt' or pattern). The place where there is info (including theory) missing, is just the place where things like conspiracy fits; precisely in order to make the pattern, aka making sense of what you do know.