Honestly of course i would not say no to keep it!
But i would be called a scammer maybe for this?
And the fact that the money is not mine makes me a bad feeling to keep it just like this hence i made this public
I think as long as you did a reasonable effort in trying to find the original owner, nobody will call you a scammer.
You could always just leave this thread online, maybe open a similar thread on reddit, and afterwards keep the BTC. In case somebody ever comes foreward and is able to conclusivly prove they're the real owner, you can still send them 0.5BTC from your own wallet as a refund.