The book on Blackwater written by the journalist Jeremy Scahill has a lot of interesting background on Prado. Also, "American Desperado" (great book, also by Evan Wright) talks about some of Prado's interesting involvement in drug importation into Florida in the 1980s.

Sounds like an interesting guy, but probably not someone you want to meet in a dark alley.

Edit:

The Scahill book is http://www.amazon.com/Blackwater-Powerful-Mercenary-Revised-...

The Wright book is http://www.amazon.com/American-Desperado-Life---Soldier-Gove...

I've read both and highly recommend them.