Check your conspiracy theory part two: double, double, boil and trouble
Does your conspiracy theory sound something like this?
There is a large number of people who practice a form of religion that demands animal and human sacrifices.
Their practices can be traced all the way back to ancient times.
They are responsible for many mysterious murders, disappearances, and animal deaths.
They especially prey on children, or require children for certain rituals.
Their rituals include immoral sexual activities.
They practice ritual cannibalism.
They use something from the victims' bodies for medicinal or mystical purposes.
They regularly cast curses.
They have special means of manipulating or controlling people's minds.
Strange medical and psychological symptoms are evidence that one has been targeted or tortured by these people.
Their rituals and holidays are viscerally disgusting mockeries of normal, wholesome rituals and holidays. Feces, urine, and blood are often involved.
Members are severely punished (physically and psychologically) for transgressions.
Members are frequently driven to suicide.
Members often lead double lives, often seeming to be good law-abiding citizens to the public.
There are numerous telltale signs that give their allegiance away; EG, strange body markings or owning things that could be used in rituals.
If evidence can't be found, it's because they have ways of hiding it.
They have ways of traveling and transporting victims to seemingly improbable locations with no one noticing.
They might believe themselves to be worshiping pagan gods, but it's actually a satanic deception.
All of these claims go back to early modern witch panic and blood libel. (There is significant overlap between these things.) You can find this kind of stuff claimed in literature like the Malleus Malificarum, A Discovery of Witches (the one by Matthew Hopkins), and the Compendium Maleficarum. You can also find information on the history of blood libel over here.