The only problem with that theory is why would you rely on a 20-year-old goofball? Oswald had skill.
Plausible deniability. The spooks know how to recruit young loner goofball types that like guns like this kid and groom them to do crazy stuff like this. The spooks know the kid will get taken out and the spooks are safe from getting caught.
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He’s expendable. We know that much.