If I was in incredible pain and wanted to end my own life but was not capable on my own I might ask a close friend to help me with that. If that friend had enough empathy to help me fulfil my hypothetical wish then they would be a murderer, but a kind and helpful one.

edit: maybe we want to define murder as killing someone who does not want to be killed. I would ask what you have to say about the "trolley problem". https://en.wikipedia.org/wiki/Trolley_problem