Yeah, this is a tough one!
discuss the role played by the first responding officer/s to a homicide scene --- spend a few paragraphs doing this. You know what this means, so just paraphrase your text book and cite it.
and [discuss] the role of the primary investigator upon notification to respond and assume case responsibility. This sounds like the sort of thing that has a section of your text book dedicated to it. What is the primary investigator supposed to do when s/he is notified of a case?
Search that text book! Answer both questions :-)