Why Conspiracy Theories Are Self-Debunking

No conspiracy theory has ever been able to explain why the conspirators left behind the clues that the conspiracy theorist has detected. The conspirators supposedly had the power to manufacture whatever evidence they pleased - to a standard that fooled entire generations of historians, lawyers, journalists, and so on - and to make the perpetrators 'corroborate' this manufactured evidence, yet they made elementary errors in their narrative such as having a 'scientifically impossible' murder weapon and contradictory eyewitnesses. How can conspirators have the superhuman ability to control all variables in the production and dissemination of evidence - without that conspiracy ever suffering any leakages - yet be unable to prevent the narrative developing the holes that only the conspiracy theorist can see?