When a doctor suffocates a terminally ill patient by putting a bag over his head, he does not help him to die. He kills, but he does not execute, since a killing is an execution only when it carries out a sentence of capital punishment. "Helping to die" applies when a person takes part in the lethal act himself, but is assisted by another, as when a doctor provides the pills, and the patient takes them.
J E J ALTHAM
Gonville and Caius College