I was under the impression that we dont negotiate with Terrorists!

I was under the impression that our US Policy does not allow us to negotiate with Terrorists.
If that is true then how come was the FBI involved with paying ransom in exchange for the release of Warren Weinstein?

Source: http://www.cnn.com/2015/04/29/politics/fbi-warren-weinstein-ransom-al-qaeda/index.html