"That is where the concept of murderous intent comes in."
He said the concept of motive was important - and jurors must not confuse it with intention.
"Motive is the reason or emotion that may have prompted a particular act… the Crown doesn't have to prove motive.
"Intention is what result the person intended to bring about - not why they intended to do it."
Justice Moore then spent time explaining the intricacies of murderous intent as described by the Crimes Act.
He said the intentional killing of another person, by law, was murder.
Justice Moore said murderous intent was when a defendant means to cause bodily injury that is known to be likely to cause death, and is reckless whether death ensues or not.
He said the had to be 100 per cent sure that the accused had murderous intent when he put his hands on Millane's neck.
"Are you sure that when he applied pressure to Miss Millane's neck…. Did he intend to cause injury?" he posed.
"If you answer is yes, then you would find (the accused) guilty of murder."
He said if the jury did not believe he intended to cause harm to Millane - he was not guilty of the charge of murder.
Again, they had to be sure beyond reasonable doubt.
"Are you sure when he applied pressure to Miss Millane's neck (he) ran the risk of Miss Millane dying… he nevertheless continued.
"If yes, then (the accused) is guilty of murder.
"In other words (he) must have appreciated Miss Millane's death was a likely consequence… but was willing to run that risk."
Justice Moore said the jury had to establish whether the killing was deliberate and intentional or the result of an act that was known to be dangerous to a person and carried out regardless.
Grace Millane murder trial: What the judge told the jury