Manslaughter is NOT Murder
I'm amazed by the number of people who have said to me (up till now from just yesterday!!) - "this is why Sri Lanka needs the death penalty - cos the courts don't give good judgments! Did you hear that the murderer in the Jonsson case got only 12 years jail time and a fine??"
YES, there is a difference.
Prosecution must show intention (=mens rea) to prove murder as opposed to manslaughter. Manslaughter is, in simple terms, where a killing happens, but without intention to kill. Of course this is a subjective element - though generally it's decided on the principle of "would a reasonable person..." which is meant to minus the subjective element.