In Colombia usually the term panfleteo references the spreading around town or just left in front of certain people's houses of short one page flyers with death threats. To use the term pamphleting or even pamphlet for this does not work well. In English pamphlets are usually in color and folded, at least once but usually as a trifold. I don't see death squads taking the time for this sort of layout and folding! Usually the sorts of things the death threats use in U.S. English we would call a flyer. But just calling this flyering in English would not carry the connotation of death threats, thus my suggestion of adding the term threatening.
This term and the false cognate jumped out at me in this powerful article, which despite this term hiccup I strongly recommend: