This is sounding oddly specific. OP, please don’t kill your family member.
Edit: Actually, I’d like to add something. If you were to suffocate someone with a pillow or poison them, both of them would point to foul play, which would instantly pull in a list of possible suspects. In that list, the ones with motive would be investigated a bit more: ie, had a spat before the death. And from the on, it would be up to match evidence, now that an investigator knows what they’re looking for, it won’t take long to put 2 and 2 together.
Funny tangent. I remember windows HRESULTS containing E_SUCCESS (error success) and something along the lines of S_FAILURE (success failure) I’m a little fuzzy on that second one though, so someone else can correct me if I have the wrong name for it.