Activation lock on repaired ipad

I recently bought a faulty ipad 4 from a company on ebay. This company has a contract with Costco where they purchase all of Costco's customer-returned faulty items. The ipad had a faulty battery and would not charge enough to allow a proper boot. I replaced the battery and managed to get it to boot properly, having done so I decided to restore the ipad - this has now resulted in an activation lock appearing when I turn on the device. I know what you're thinking - stolen! I am pretty certain this isn't the case, first I have the ipad in its box with all accessories and the serial number on the box matches that on the back of the ipad; secondly, I asked the company I purchased the ipad from to supply me with proof that it came as part of a batch of faulty items from Costco - I have a receipt for this, also Costco have provided proof that they supplied the item. I have checked that the ipad has not been listed as stolen - it hasn't. The only problem I have now is in trying to trace the original owner so that I can ask him/her to remove the ipad from their icloud account. I feel that Apple should do something in this case as it is obviously a legitimate situation. Does anyone have any advice?