I think it should be forgiven, it is only a single act that does not define the person, though it is obviously a huge act which will have ramifications for everyone involved and the person who committed it.
I just don't think an individual life is that sacred, if it were I would simply die myself from the despair of people dying for no reason, rather than there actually being a reason (no matter how poorly reasoned) in the case of a murderer.
I think life is precious and frankly, fan-fucking-tastic, I think life is the greatest thing about the universe (biased I know) and humanity perhaps the best example of it. But an individual life, not so much, I would do more towards the affirmation and strengthening of life, to take life as far as it can go, not merely protect individual lives or condemn through resentment someone who takes another life.
I recommend reading Crime and Punishment, if you haven't already, fascinating reading on this kind of issue, and by no means is the murderer right, but I think he is in some ways forgivable.