The circumstances of Eric's uncle's death are not mysterious. Only the why it happened: that's unfathomable.
Possibly the common link is the archives, the physical evidence that floats up across time, that had been waiting there all the time. For Eric, it was the discovery of a tangible thing, his uncle's WWI decoration. For Auster, it was coming face to face with old newspapers:
The facts themselves do not disturb me any more than might be expected. The difficult thing is to see them in print--unburied, so to speak, from the realm of secrets and turned into a public event. There are more than twenty articles, most of them long, all of them from the Kenosha Evening News. Even in this barely legible state, almost totally obscured by age and the hazards of photocopying, they still have the ability to shock.
Auster's book begins with a sentence from Heraclitus: "In searching out the truth be ready for the unexpected, for it is difficult to find and puzzling when you find it."
Robert Frost had the same idea.