No. Two reasons: the person has taken somebody's life. Murder doesn't just affect the victim, it affects the victim's family, friends and to some extent, the offender's family. To help him die would be to absolve him of his crime, and possibly cause more heartache to those who are left behind. Euthanasia for offenders' is just an out so they don't have to spend years inside. They did the crime, they should pay for it (not with their life, that achieves nothing).
Secondly, one of my favourite quotes: the problem with an eye for an eye is that the world ends up blind. In this case, euthanasia is murder (I do agree with it for terminal illness though). Considering that quote, if everybody who ever killed someone had to die then there wouldn't be many people left.
If you help a murderer die, where do you stop? Do we help convicted paedophiles or terrorists die? (Rhetorical)
I know euthanasia is a controversial subject; this is my opinion and I don't want to get into a debate about the ethics, morals and whatever else you can think of on my opinion