Bought a locked iphone 5s. Can I trade it?

I was mugged and beaten a week ago. The theifs took my iphone 4s. I have no insurance for it. My uncle got me an iphone 5s that he bought on Craigslist. It starts off like a new product, but asks for the original apple id. The previous owner got it from his mother, who doesn't know the id. Can I trade it at Apple or AT&T for a new one? Or trade it to lower the price of a new phone? I need a new phone. PS: We bought the phone, we have the receipt and everything. I don't wanna switch the motherboard, it's too expensive

Make sure you activate find my iphone on the 4S that was taken, it will make it unusable. On the 5S his mother will need to reset the ID / pwd and then wipe it (she can wipe it remotely also with find my iphone). Then you can set it up as your own. Always verify this before buying.

Do a Full Recovery on it and it will work.

If the seller can't unlock the phone with the Apple ID, it's stolen, no matter what his story might be. And you can't reset the phone without the Apple ID. The Apple Store and AT&T will not help you with a stolen phone (nor are they able to do so). So you've essentially purchased a paperweight. You would have been better off paying more for a legal phone that you can use, since now you've paid less but for an expensive doorstop.