Actually, it's the 'public interest' against the defendant. The 'public interest' is represented by the Crown.
Good luck with that. I have personally heard a Crown make personal emotional references in a Courtroom, that neither the Duty Counsel, nor the Judge challenged.
In this case, it was manslaughter. Intent, not circumstances makes all the difference. In the latest case, with the young offender, it will be the same ending, manslaughter. Because neither had intent.
Public Interest or the Crown, it is ultimately the same thing. It is society as a whole. Far better than the family being the one to prosecute.
Emotional arguments should have no place in a courtroom, or really anywhere where good arguments are taking place.
Also, is not intent one of the circumstances?