When the German cannibal Armin Meiwes was on trial, it was actually a legal conundrum. Meiwes' victim had explicitly consented to being killed and eaten, even dictating how he wanted to have it done to himself. So was it murder or more of a convoluted version of assisted suicide ("killing on demand" is the legal term in Germany)? He was eventually convicted of manslaughter and got a prison sentence of eight and a half years, a few years later changed to a sentence for life.
there was a case a short while ago here in sweden where a husband did assisted suicide for his wife and the court kinda just immediately went "oh yeah that'd be ameliorating circumstances for sure" when her letter was presented, i'm quite surprised at how everyone seemed to be on the same page.