From a Globe and Mail Article:

A reputed leader of Colombia's biggest drug cartel radically altered his facial appearance with repeated plastic surgeries. But his own words gave him away, thanks to advanced voice recognition technology that has become a key tool in the war against drugs and terrorism.

U.S. agents confirmed the identity of Juan Carlos Ramirez Abadia using the equivalent of a vocal fingerprint, his attorney said Friday.

Background on voice recognition (from Wikipedia): 

Speaker recognition, or voice recognition is the task of recognizing people from their voices. Such systems extract features from speech, model them and use them to recognize the person from his/her voice.

Note that strictly speaking there is a difference between speaker recognition (recognizing who is speaking) and speech recognition (recognizing what is being said). Generally these two terms are frequently confused and voice recognition is used as a synonym for speech recognition instead.

Ken 

--- (Edited on 8/10/2007 10:47 pm [GMT-0400] by kmaclean) ---