If it says "discuss liability of John relating to involuntary manslaughter" then you don't need to discuss murder.
If it says "discuss John's liability for homicide offences" or simply "discuss," then you need to get murder out of the way for completeness' sake.
You really can get murder out of the way in a four-minute paragraph, if it's clear that the question doesn't relate to murder- just make sure you give a rock solid reason why murder is out of the question, and move on.