There really aren't enough facts described to make a judgement either way, but regardless, when an officer of the law uses lethal force, you can be assured an investigation will follow.
Unfortunately, even if the details become public, it will not 'unkill' the apparently feeble-minded individual who failed to consider the
consequences of brandishing a toy as a weapon.
Fault is easy to attribute from the chair in front of my computer. I hesitate to reject the possibility that this was justified, but I do not
hesitate to lament the death which, as most involving gunfire, was probably avoidable.
Calling it "murder," however, is hyperbole. Unless someone has weighty evidence to indicate that intent to kill was pre-existing.