chain complexes

Dear Categorists - Who first showed that an internal category in the category of abelian groups was a 2-term chain complex of abelian groups? What's a good reference? Who first showed that an internal strict omega-category in the category of abelian groups was a chain complex of abelian groups? What's a good reference? (Of course for "internal X in the category of Y's", I am willing to accept "internal Y in the category of X's" as a substitute.) Best, jb