I'm guessing that death is a 'better' alternative because most killers like Spector or West are addicted to what they do. In fiction or in reality, it is a compulsion that needs to be satisfied. Perhaps the prospect of years, decades ahead of them where that compulsion can never be satisfied again is too much to contemplate. So as a last demonstration of their 'power' they kill themselves. I'd like to say that they're cowards talking the easy way out but I'm not convinced that suicide is easy...
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Good ending. We got the details of what drove Spector to be the killer he became. I thank the gods we didn't have a long, drawn out trial with a slippery lawyer trying to get Spector off on a technicality and I'm glad that Stella's dream diaries didn't get picked apart in court and therefore in the press. And if there is a series 4, we don't have to suffer more Spector.
Felt sorry for Wallander man... but really, the security, staffing and procedures certainly need to be tightened up.