[WarDekar]

You're thinking of Assassination markets [0]

[0] http://en.wikipedia.org/wiki/Assassination_market

[gwern]

I find assassination markets a fascinating concept: I wrote a short story about them ( http://www.gwern.net/fiction/The%20Ones%20Who%20Walk%20Towar... ) and pondered whether they might be a successor to Silk Road (http://www.gwern.net/Silk%20Road#future-developments probably not).