For example, right now, in one of India's jails lies a man named Ajmal Kasab. He is one of the terrorists involved in the 26/11 attack on Mumbai. He was caught on tape mercilessly killing people with his AK47.
If you do away with the death penalty entirely, how do you execute this fucker and others like him?
http://en.wikipedia.org/wiki/2008_Mumbai_attacks
Edit: A lot of people asking similar questions. So I'll just answer them here.
Being identified by eye-witnesses and being caught on camera are not the same thing. People make mistakes while remembering. Cameras don't. Further, he was apprehended by the army/police in the middle of his killing spree. There is NO WAY it was someone else.
Handing him a life imprisonment just puts the system at risk. It will just lead to terrorists resorting to kidnap to release him as has been done in the past. A well known example: http://en.wikipedia.org/wiki/Indian_Airlines_Flight_814