go for it, gl (for your assignment that is!).
There are three types of homicide which are murder, voluntary manslaughter and involuntary manslaughter. I want to clarify what these are. Then I will try to explain why self-defence can't really be used for involuntary manslaughter.
The actus reus elements for all homicides are contained in s18 Crimes Act 1900 (NSW). The actus reus elements are: act/omission, causing (causation), death, of a human being. Each of these is a separate element and they all have to be present.
The mens rea elements for murder are also contained in s18. The mens rea elements are: intent to kill, intent to inflict GBH (really serious injury), recklessness (foresight of probability of death), and constructive murder (during 25+ crime). Only one mens rea element needs to be proved.
If these elements are made out, murder can be proved. But during a trial
the defendant can bring up a partial defence and have the charge reduced to voluntary manslaughter (which just means a lesser sentence). Some of these partial defences are provocation (s23), substantial impairment (s23A) and excessive self-defence (s421). Other defences are self-defence (s418), mental illness (M'Naghten), automatism (Ryan) and intoxication (s428C) - which are complete defences.
If the prosecution do not intend to charge murder, they can charge another form of homicide known as involuntary manslaughter. The two types of involuntary manslaughter are manslaughter by unlawful and dangerous act, or manslaughter by criminal negligence.
The mens rea elements for manslaughter by an unlawful and dangerous act are in the name. The act (it can be an omission too) must be unlawful and it must be dangerous. Whether it is unlawful will be judged by whether it is a criminal offence (which it has to be) and whether it is 'unlawful in itself' (this test actually isn't helpful). Whether the act or omission is dangerous will be judged by whether there would have been an
appreciable risk of
serious injury to a
reasonable person in the
offender's position (I've underlined the key parts).
The mens rea element for manslaughter by criminal negligence is completely objective (it does not take into what the defendant was thinking at all). Criminal negligence involves such a great falling short of the standard of care which a reasonable person would have exercised as to merit criminal punishment. And in the case of manslaughter by criminal negligence, it must involve a very high risk of death.
Those are basically the types of homicides in NSW and the types of defences. I haven't actually seen the question that we're talking about and I assume that the person was being charged with involuntary manslaughter. On that assumption I want to explain why I don't think self-defence applies to involuntary manslaughter.
The person may be charged with a manslaughter by an unlawful and dangerous act. My casebook says that according to Cornelissen [2004] NSWCCA 449, an act performed in self-defence can't be an unlawful act. Therefore the elements to unlawful and dangerous manslaughter are not made out. I think what my casebook means is that the self-defence will act as a defence to the dangerous act, rather than the manslaughter.
If the person is charged with manslaughter by criminal negligence, I can't see how he/she could claim self-defence. Remember, manslaughter by criminal negligence involves a very high risk of death and such a great falling short of standard of care as to merit criminal punishment. Acting in self-defence would probably not be such a great falling in the standard of care as to merit criminal punishment. Acting in self-defence is expected of the reasonable person. Therefore the elements are also not made out (I am speculating here; I don't have any authority on this).
Look, I haven't seen the question. I just spent like 30 minutes writing this out, and this is all beyond legal studies. I seriously got logged out in the time it took me to type this. I suspect that if self-defence was the option that you thought was most likely right probably is right. I hope this clarifies things. I know it clarified things for me, and I have an exam for this in 1 week :|