It might make him famous, if he had a way of proving his story before being eliminated or otherwise coerced into silence. But he could have known about the existence of UFOs and not have been able to provide evidence.

And maybe he never had any desire to "blow the whistle" in the past (thought it was perfectly legitimate for the government to keep the UFOs secret), but has since changed his mind.

Hypothetically, of course.

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"All your bias are belong to us." Ara Pacis
"A witty saying proves nothing." Voltaire