How would the examiner mark my exam? Do i have to write everything about murder to get full marks?

It depends on if it is a scenario question or an essay question. With scenario questions you mainly have to apply areas of murder that have relevance to the scenario question. For example if there is nothing to do with omissions or life machines, there is no need to explain if a human being would regarded as someone who is in a life support machine, just refer to what the scenario is telling you, that's how you gain full marks. Don't forget that you have very limited time to read, highlight and answer the scenario question so writing everything would not help with your timing but picking the relevant factors would really enhance your answer. With essay questions again you have to read the question and answer accordingly to the question given. Don't go off board otherwise the examiner would notice. Essay questions on murder would usually refer to the reforms so make sure you have at least 3 points for that.