The presupposition that he was a "low IQ aircraft mechanic" is only a theory a team of empty pretentious government suits could put forth. To this day that is what still inhibits the FBI. They are merely drones but they think they are the queen. They can't think outside of their cubicles or beyond their degrees. They assume that an Einstein or Tesla clone would be teaching at a nuclear physics lab simply because they can. They can't fathom that maybe the most brilliant people that currently exist in the world right now could be some person working at a local cafe serving you your morning coffee, or a recluse unknown to anyone, or a car mechanic and the reasons they do these things are not because those are their only options, but because they are places they want to work at, places they choose. Places where they can experience authentic human interactions. They are happy because they are not the automatons and droids that the FBI agents(But think everyone else are the droids) are, they are doing what they want to do, and earning only what they need. They are happier than people that try to compete with everybody else. Profilers presuppose so much that turns out to be so inaccurate. Profilers really don't understand people, not everything is about data and forensics. Never assume anything, expect everything and nothing at the same time. Sun Tzu understood this.
One of the agents used the "to a hammer everything looks like a nail" analogy. Ironically the FBI itself is guilty of this mindset also except to the FBI everyone that LOOKS like a criminal is a criminal.