Can you find his address on 2016-2017? if you can find it and he can sign a message, then this case will closed.
Yes, he has one bitcoin wallet number for 2017. Although this message has been deleted and is archived in the forum, I think that for many of the doubters here, signing from this wallet would be good proof of account ownership.
https://ninjastic.space/addresses?address=1XpJRma2pY9CjGdfQPEprohiFETrnbU4JHowever, you can predict that the story of the loss of this wallet and all the other excuses will begin.