Just for discussion, "Odohu" your approach is the best way forward which in my shoe will likely do same thing, only a theft whose mindset is centered on how to collect and scammed people asset will even think contrary without even making trial to see if he can reach the owner, the amount mentioned is big for an investor to accumulate such mostly those that don't have diverse means of income,you should know what the owner goes through to get such seen it as opportunity to divert is dangerous redline to Cross, not every open door is a signal of door been opened, it can also be a trap where lack of selfcontrol will end one with miserable way of life.
The mindset of sending the Bitcoin into another fresh wallet he can control is better, it will give you the control over the Bitcoin since its a guess work according to the discussion, but trying to trace the owner of the Bitcoin is the problem I see here. There is no way to find the rightful owner of the Bitcoin because no one will prove he owns it by showing the private key or his/seed phrase publicly looking for hack their wallet or so.
Furthermore, this is not the only Bitcoin forum, and so people dont know about this forum, I could have say that they can trace it here for you to maybe handover the Bitcoin back if you find the rightful owner of the Bitcoin.
This is just a framed story I think because guessing private key or seed phrase is something I dont think is possible at all, so we cant say that this is correct, but if it happens to me, I am holding the Bitcoin because so many lost private keys or so many wallets that contained Bitcoin in them are like lost Bitcoin , and this is another reason why Bitcoin value will keep going up.