If they have been found guilty, then they are not innocent.
Not always, they could have been framed. Just because they've been found guilty by the law doesn't mean they are actually guilty.
This is why I disagree with imposing death penalty as punishment. There are a lot of people who are prosecuted and incarcerated for the crimes they did not commit. In my opinion, Blackstone's formulation in criminal law which states that, "It is better that ten guilty persons escape than that one innocent suffer", is in line with this situation. This is because we could not take back the suffering we had already inflicted to another, or bring back a life already taken.
Plus, in Hinduism, there's something they call the Karmic cycle. Some defines karma as what goes around comes around, or what one send out in the universe is returned to back to the sender, sometimes a hundredfold. IMO, by imposing the death penalty, we create karmic energy that brings the past pains, in this case, death and suffering, into the future, which is higher crime rates. The cycle continues, until it is broken, say, by not imposing death penalty.
Well, that's my two cents about this topic. Sorry if the last bit is jumbled up and confusing. I've only started reading about Hinduism and Buddhism last month. :\