The true identity of Bitcoin inventor Satoshi Nakamoto may forever remain a mystery after Dr. Craig Wright backed out a plan to provide further proof that he is the man behind the mask.

Wright, an Australian academic and inventor, went public on Monday to confirm last December’s media reports that he was Satoshi, the pseudonymous creator of the Bitcoin crypto-currency and its underlying Blockchain technology.

Doubters immediately found fault with Wright’s claims, just as they’d failed to be swayed by the earlier media reports. On Wednesday, Wright vowed to provide further proof that his claims were legitimate by moving Bitcoin mined from the very first blockchain blocks, which, at the bare minimum, would have demonstrated that Wright had access to the digital keys used by the Satoshi identity.

But by Thursday, Wright had an apparent change of heart. In an emotional post to his personal blog, Wright said he’d initially believed that he could “put the years of anonymity and hiding behind me. But, as the events of this week unfolded and I prepared to publish the proof of access to the earliest keys, I broke. I do not have the courage. I cannot.”