Locked Out Of iPhone 4? Can't Contact Previous Owner?

I recently got an iPhone online. I can't contact the owner and the phone is still linked to their Apple ID. So, I can't use it. I already tried recovery mode. Didn't completely erase the phone. Still need Apple ID from previous owner. Can anyone tell me how to COMPLETELY erase it so I won't need the Apple ID or a passcode? I would truly appreciate it!

Nope. You got scammed.
What's the point of an anti-theft system if you can easily bypass it?

You don't, you got scammed and bought a phone that was reported lost or stolen. You didn't buy it from the person who's Apple ID you need. So you are SOL, and out the money. Sorry. Better luck next time.

But if you really want to contact the owner, take the phone to any Apple store, they can get in contact with the owner using the Apple ID or the phone's ESN or IMEI. Ask them to give the owner your contact information so you can set up getting them to remove the phone from their account. They may do it, then again they might not, but if you don't ask, you are stuck with a brick.

You can't. Unfortunately you may have been scammed.