Lone nut
The lone nut is a fallback position for weavers of the official narrative, for tying up loose ends. Blaming a single individual gives closure to an otherwise annoying narrative without needing to investigate systemic forces at work.
Official Narrative
Lee Harvey Oswald, Gavrilo Princip, Bruce Ivins... History is replete with lone nuts, who all decided to act independently of any organisation.
Problems
Many of these so-called 'lone nuts' had close connections to the security services. Mounds of evidence exist that some they were not acting alone and that others did not act at all, but were set up as patsies.
Patterns
Several 'lone nuts' meet early deaths - sometimes soon after their public identification, such as Lee Harvey Oswald, sometimes before they have even been identified as such, such as in the case of Bruce Ivins.