The word "responsible" works as an adjective only. What is a noun for a person who bears some responsibility (i.e. is accountable for something)?
Note: Originally my question was longer, but the added context seemed to mislead people into providing the wrong answers. I have edited the question and removed the superfluous information.
Best Answer
I would just say "responsible person." Where I work, we assign tasks to the appropriate person for each item in any of our action lists. That person becomes the "responsible person."