According to present authorities, there are two lines of reasoning. The first is that E and F are principals of this crime, not accessories, in that all aim at killing A and what each does is the performances of his separate but related function in order to accomplish the common aim. It is a case of division of work.
The second line of reasoning takes the opposite view. The degree of E and F’s involvement is to a limited extent. They have not done anything that is intrinsically harmful to A. Facilitation of a crime should not be punishable to the same extent as actual commission of it. Without E and F, D could have accomplished his job by finding other persons to do their work in their stead.