spelled out.
One of those is the definition of murder that you are using.
Merriam Webster's relevant definition is:
https://www.merriam-webster.com/dictionary/murder
1: the crime of unlawfully and unjustifiably killing a person
Wikipedia's definition is a little more involved:
https://en.wikipedia.org/wiki/Murder
Murder is the unlawful killing of another human without justification or valid excuse committed with the necessary intention as defined by the law in a specific jurisdiction.[1][2][3] This state of mind may, depending upon the jurisdiction, distinguish murder from other forms of unlawful homicide, such as manslaughter. Manslaughter is killing committed in the absence of malice,[note 1] such as in the case of voluntary manslaughter brought about by reasonable provocation, or diminished capacity. Involuntary manslaughter, where it is recognized, is a killing that lacks all but the most attenuated guilty intent, recklessness.
I think the ultimate law involved, however, is God's law, upon which all other laws should be based, or at least in harmony with.
Our Lord's 5th commandment is:
Thou shalt not kill
Which has been historically interpreted/defined to mean, Thou shalt not intentionally kill any innocent human being.
I believe that should be the bottom line criteria in any of these discussions.
"Cutting off" food and water implies that the caregivers are either disconnecting the feeding tubes or, unlikely in the situation you describe, preventing others from feeding them or giving them hydration. To my mind, this is the intentional killing of the unconscious individual. I believe that would be gravely immoral on an objective basis, but it would be up to Our Lord to judge the decision maker's heart as to what they knew and understood and how culpable they might be.