From Nagarjuna's Treatise on the Great Perfection of Wisdom
(Dharmamitra Translation)

What constitutes evil? [In the case of killing], it is where there actually is a being, one knows it is a being, one brings forth the thought desirous of killing and taking its life. One then does generate the physical action. [It is a case where] there does exist a created form. This constitutes the offense of killing a being. The other [actions]: the tying up, the confining, the whipping, the beating, and so forth,-- These are dharmas which are auxiliary to killing.

Additionally, one incurs the offense of killing when one kills another [being]. In a case where one kills one's own body, if one knows it to be a being and then performs the act of killing it is not the case that this constitutes the offense of killing.

It is not [a killing offense] when one sees a person at night, thinks him to be a leafless tree trunk, and then kills him. When one deliberately kills a being one incurs the killing offense. It is not the case when the act is not intentional. When one kills a being and does so with a pleased mind one incurs the offense of killing. It is not the case where one is in [a state of] crazed delusion. It is when the root of life is cut off that it constitutes the offense of killing. It is not the case that the physical action of creating a wound [in itself] constitutes the offense of killing. It is not the case that only giving verbal instructions as an order that the verbal instructions [in themselves] constitute the offense of killing. It is not the case that the arisal of the thought alone [constitutes the killing offense]. Cases which accord with these criteria constitute the offense of killing. When one does not create these offenses it constitutes [remaining in compliance with] the precepts.

In a case where a person takes the precept, the thought arises and the mouth speaks, saying, "From this day I will not again kill beings." If the body does not move and the mouth does not speak and yet the mind alone arises and one vows to oneself, thinking, "From this day on, I will not again kill beings," this does constitute the non-killing precept.