Q: Advise from in the dark

I have never learned much about computers other than turning it on and looking at stuff on the internet, buying from Amizon, doing the email thing, etc..... At a yard sale I purchased a computer called a Mac Book Pro. Looking up the serial number I found it was from mid 2010 13inch. The problem it had is the guy said he forgot the password. I followed instruction online to get through that and got it to except me as the new administrator and who ever the previous owner was is now the guest. Thing is not all is working. It has a bunch of the previous owners personal stuff still on it but you can't access any of it. I am sure this computer is stolen otherwise the stuff would have been deleted. Everyone thinks I am stupid to want to find the owner and return it to them because the last time it was active was 2012 and they most likely moved on to another computer and , well, you get the picture. But that is just the way I am. Is there anyone that could take over this computer remotely and either find who owned it or if that is not possible then to format it so I can then use it myself? I have a disk with it but don't know what to do? Please advise or help me. My preference would be to return it to the owner. I don't know what to do and I don't know if this is something to address here and I apologize if not.