New phone

Not only is there not a way to "legally unlock" it, there is not a way for you to "legally" keep it.

Google "theft by finding".

Turn it over to the police. It doesn't belong to you.

Failure to do so may constitute a criminal act.

No. That is the purpose of the Activation Lock to prevent anyone but the owner from using it.

It isn't yours so turn it into the Police.