Mercy-killing
Aside from these rare cases killing cannot be justified. Killing is killing even if it is called mercy killing. As the means for killing nowadays has become easily available one has to wonder whether the so-called mercy killing is truly for the sake of the patient or for those who accept killing and encourage it. There are cases in which the motivation to save self from suffering (e.g. getting rid of one's own repugnance with the suffering of the other is stronger than the motivation to save the other.
In the light of such understanding Buddhism strongly opposes assisted suicide. In the Buddhist view assisted suicide is not an act of compassion as claimed by many people. Killing always brings bad karmic results both to the person who is killed and to the perpetrator. When requested by patients to assist them to end their own lives Buddhism advises us instead of acting upon the request we should try to find different available means to ease their suffering according to the kind of suffering, physical, emotional or psychological, the patients are undergoing. Such is the way of genuine compassion.