Ask HN: How to unlock an iCloud locked iPhone

So I Purchased this phone from a guy from Craigslist, an iPhone 5S. Its in brand new condition and is all good except it is iCloud locked. The person who sold it to me refuses to answer his phone. I was hoping is someone knew a way to unlock it. Please help. If you do not want to reply here, you can email me at garg.ankit@hotmail.com.

Any help would be highly appreciated.