Lost & Found - BRICK
Unfortunate that the original owner could not be found.
Apple has deliberately designed the device to be linked to an individual. Without that individual's involvement, the security will not be bypassed by Apple without a court order.
Consider returning the phone to Apple for parts recycling:

Recycling an Apple product should be as easy as using one.
The Apple Renew program lets you recycle your device online. We’ll make sure it’s recycled responsibly or given a chance to be used again.