In related articles like this one:
http://ap.google.com/article/ALeqM5hpvMdtVTcNcKaoBNpSksm6MfTIegD94CER7O0
..they refer to evidence from transport lists, so this isn’t just eye-witness, this is period documentation.
The period documentation clearly proves that Ivan the Terrible was a mass murderer, but it doesn't prove that this guy is Ivan the Terrible.
Israel concluded he wasn't. I just wonder what the new information is that says otherwise.