I remember, on the road got in the hands of a widebody - the book of D. Donzova. There in the course of the plot was poisoned with ethylene glycol, spilled into a bottle from under the juice, for example. Ethylene glycol is sweet and odorless. Ready "recipes" for killing the lady scratches. It may not be easy to get this liquid, but nevertheless...

A huge amount of poison is quite easy to get or do. Identifying the cause of death is quite simple.
And if the poison is easily detected, then there is no difference between poisoning and a blow to the head. Unless you’re a poison maniac and you’re killing strangers in a burger king.