Thomas Fuchs, MD, PhD, Associate Professor of Psychiatry at the University of Heidelberg, wrote the following in his 1998 article "The Notion of 'Killing'. Causality, Intention, and Motivation in Active and Passive Euthanasia" published in the Journal of Medicine, Health Care, and Philosophy:

“We may discern a relevant difference between killing and letting die on the level of causality, namely if we consider the biological dimension… Only on this biological…level are we able to obtain the proper notion of killing: It is an impact extraneous to the organism, produced by the action of another person, and causing immediately lethal damage. ‘Letting die’, on the contrary, means to give way to an ongoing inner-organismic process of disintegration, without supporting or substituting vital functions. Therefore the extubation [removal from a ventilator] of an incurably ill patient, though a physical action with subsequent death, is not killing in its proper meaning. Only by active euthanasia does the physician become the actual agent and cause of death… The extubation does not produce the effect of death; it only influences the time of its occurrence.”