Are you talking about a carrier locked iPhone or an iCloud activation locked iPhone?
If the iPhone is carrier locked, the first thing to do is ask the carrier if they'll unlock the iPhone for you.
If the iPhone is iCloud Activation Locked, I'm afraid that without the iCloud ID and password of the original owner, the iPhone can't be unlocked.
In addition, I've moved your post to its own thread, where it will receive more attention.