Purchased iphone 5 on craigslist i lost contact with owner restored phone and know it is i cloud locked what can i do? May i some how unlock it or its a useless paperweight?

If you turn on the device and you're asked for the previous owner's Apple ID and password, the device is erased but still linked to the previous owner's account.

Turn off Find My iPhone Activation Lock - Apple Support

If you cannot longer contact owner, check with Craigslist for a refund. If you are unable to get a refund then you have a paperweight.