I was using murder in a colloquial sense, not a legal one. I'm pretty sure in England the legal term for what was done to Turing is constructive manslaughter (http://en.wikipedia.org/wiki/Manslaughter_in_English_law#Unl...). But IANAL.
The legal term would be something like "proper application of criminal law". You can't claim that it was constructive manslaughter to apply the law at the time.