I have no reason to believe the authors aren't honest people who worked hard and firmly believe what they wrote, BTW.

But they're also members of the MIT community, and Abelson at least is a professor first and investigator second; that's going to affect the investigation process and conclusion.

That's why when there are big investigations in government, they often go hire an outsider as inspector general or independent counsel; there's no substitute for independence, complete access, and an investigator's skills and mindset.