in theory holder's weapon theory is quite sound coz there are no marks left behind. Of coz we all know tht it's the government ordered type of hits tht are the perfect ones coz the media will know abt it but the case will be go unsolved or labelled as accidental death.
For me it would be sort of like a long one. Create an illness within their body. When you know wut they eat everyday, use tht to ur advantage n use the ingredients in tht food to increase the illness.
Or you just do it old school mafia style, get their car rigged with a bomb. This would of coz only involve ppl who are single.