Honestly?
I think he only needs a few years. Why? He's not a threat to society, and I'm sure he'll learn his lesson very quickly. He never showed an intent to murder, and, while his actions are reckless and reprehensible that a manslaughter conviction is appropriate, anything more than that would be wasting space in already crowded prisons.
The prison system should be about rehabilitation, rather than revenge and punishment. Of course, that is often easier said than done, but this man in question should be fairly easy to rehabilitate.
Melon
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"He had lived through an age when men and women with energy and ruthlessness but without much ability or persistence excelled. And even though most of them had gone under, their ignorance had confused Roy, making him wonder whether the things he had striven to learn, and thought of as 'culture,' were irrelevant. Everything was supposed to be the same: commercials, Beethoven's late quartets, pop records, shopfronts, Freud, multi-coloured hair. Greatness, comparison, value, depth: gone, gone, gone. Anything could give some pleasure; he saw that. But not everything provided the sustenance of a deeper understanding." - Hanif Kureishi, Love in a Blue Time