Previous owner

It's no good your saying that, you've been told the exact truth. You are never going to be able to unlock the phone, and you are never going to be able to find the previous owner. Even if Apple knew who it was it would be against the law for them to tell you. If you think it is stolen you should turn it in to the police. You are not going to be able to use it anyway.

If you believe the device to be stolen, then you must turn it into the police. In many jurisdictions, the mere possession of an object believed to be stolen property is a crime in itself and can cause you to be charge and prosecuted.

No, if it's activation locked it's useless to you. Turn it in to the local police.

No, Apple will not provide such information to you.

It might not be helpful but that is the way it is. You are not going to get any information on the owner of it. So turn it into the police.