I thought murder was the killing of a human by another human?
No, the killing of a human by a (legal) person (which includes both natural persons and all other things subject, in their own being, to the law as an actor rather than mere property, such as corporations) is homicide. For the question to even be coherent, one must presuppose that HAL is considered a legal person — a subject of legal responsibility — but humanity is not required.
Murder is unlawful (phrased another way, “without legal excuse”, self-defense is an excuse, for instance) homicide with malice aforethought. (“malice aforethought” includes, but is not limited to, intent to kill; see, e.g., the felony murder rule, depraved heart murder, etc.)
That you A. Carried out the act; typically known as the Actus Reus, and That you B. Had the guilty intent or mind, typically known as the Mens Rea.
This is why the defense of "insanity" exists in so many legal systems; if you were insane you cannot satisfy condition B and therefore cannot have committed a crime such as murder, even if you performed the act of killing another human while insane.
However, this is a very accademic distinction in practice in most places. There is usually a second slightly lesser crime known as something like "Manslaughter" or "Culpable Homicide", which is in essence a Murder charge without B - you killed someone but it was an accident for example - you didn't actually mean for them to die. Such cases satisfy the Actus Reus but not the Mens Rea of murder, and are therefore often known as a crime other than "murder" itself.
The above is an absolute butchering of Western Criminal law practices, but the general distinction between the action and the intent to perform the action is found in a lot of places, and a Murder charge often requires prosecution to demonstrate both Actus Reus and Mens Rea or the charge cannot stand. The Manslaughter charge is sometimes the fallback position for when proving Mens Rea beyond reasonable doubt for Murder fails.
The elevator pitch for this entire article is really, "Was Hal capable of mens rea - yes or no?" So far no machine has ever reached that bar, at least to my knowledge! No one really doubts a machine can do the actus reus - of course it can.
> https://en.wikipedia.org/wiki/Actus_reus
> https://en.wikipedia.org/wiki/Mens_rea
And good luck getting an investigator out to Jupiter to gather evidence for the prosecution.
In England for example the requirement for Murder is you intended at least "grievous bodily harm" and the victim in fact died.
For Attempted Murder, the intent proved must be Death, but for actual Murder, there is no need to show that the perpetrator specifically intended death.
If it's not intentional, it's not murder, it's an accident. If it is justified, then it isn't murder, it's e.g., self-defense. If the creature killed isn't sapient, then it isn't murder, but it might be animal cruelty.
Note that in order for it to be intentional, the killer must also meet some criteria for sapience, but that's not necessarily the same as being human. For example, in English translations of the Bible, Jesus refers to Satan as "a murderer from the beginning." (John 8:44)
I have not heard the definition to be about a sapient being. I always thought it would need to be a human killing a human. Perhaps in fantasy novels it can be a dwarf killing an orch, but in the real world I don't think anything else qualifies. If we include AI in this definition, we put AI above animals, which I think is a stretch for the forseeable future.
This is maybe less obvious if your government intentionally kills its own citizens for some reason and you've found it important to draw a moral distinction between "We pay government officials to deliberately kill people" and "Murder" but I have no problem saying that's the same thing, stop doing that.