Sorry, not buying that diminshed responsibility, anguished grieving, I-didn't-know-what-I-was-doing stuff!
Community living, no matter what country you live in, relies on people making good choices that don't harm others regardless of their emotional state. Otherwise, let's get rid of all our laws and act on our animal impulses.
When someone like this Russian takes it upon himself to inflict the kind of damage he did to the controllers family, we get anarchy. If he gets out in a few years and has another traumatic episode that triggers another killing, do you want to be on the receiving end?
And what's this " group of people that have have far more insight into the law than we as normal people have?". If you mean that they can recite the law better, I concede, but if you mean that legislators around the world draft good laws and deliver just verdicts faultlessly, you've got to be kidding!
I know the awful feeling that comes from a terrible loss but this ATCO and his family did not deserve this. I hope the appeal court gives the Russian life and throws away the key.