Some of those who were there had relatives who later gave what they claimed were accounts passed on to them (this happened mainly in the 1930s-1950s). But on the whole, these extra accounts (I think there might have been 3-4) were not from eye-witnesses, and made a number of highly contradictory claims (even contradicting themselves internally) that make their content suspect.
I would say, with some hesitation, that only Hoyos was close to telling the truth, but even there, we know he included erroneous information and also likely invented part of his story to protect himself, as hopefully we'll show in the book.
The real keys in attempting to reconstruct this (at least for us) were twofold: a full psychological analysis of Rudolf, Mary and those around them (thankfully we had a forensic psychologist who had consulted with the prosecution in the Jody Arias murder case to go over everything in detail), and the forensic details surrounding the deaths. Although I don't necessarily find her that sympathetic, my opinion of Mary has changed, because she was being used and victimized by everyone (Rudolf, her mother, Larisch, etc.). And she was, after all, a 17-year-old girl, immature and full of misplaced romantic notions that would never have occurred to the jaded Rudolf.