I was looking up, and finally found, the pathway for the production of HCN in the interstellar medium in the wiki article on HCN. All well and good I'm sort of happy with what I found.
But as I was reading the rest of the article they mention something I think is wrong. When HCN is used for executions, the wiki article says the principle ingredients where sulfuric acid and potassium cyanide.
I always thought it was hydrochloric acid and potassium cyanide. You know, to produce hydrogen cyanide via simple substitution.
https://en.wikipedia.org/wiki/Hydrogen_cyanide
Third paragraph from the bottom.