If we consider an inertial reference system, that is, a system in which the laws of motion comply with Newton's laws, we will have that the speed of light will be the same in all those frames of reference. In other words, the speed of light in a vacuum will be independent of the movements of each of the observers.
Under this premise he/she measures the speed of the laser light to be equal to the speed of light, because the light travels at the same speed in every inertial frame of reference
