Don't even think about it - or, rather, do!
"You shall not murder." Exodus 20.13
The Hebrew verb used here makes it clear that the prohibition is against the premeditated and deliberate killing of one person by another, as distinct from accidental death and the more indiscriminate killing caused by war. Jesus expands the terse command in Matthew 5. 21-26, where he reveals that murder has roots. It begins when a person nurses ill feelings against another. These ill feelings do not have to result in murder but murder is one of their fruits. So to avoid murder we must check our feelings, especially when they err towards dislike.
So far as they go, this commandment and Jesus' commentary upon it are clear enough. But what happens as the scenario develops to include more ethically controversial killings such as: euthanasia, abortion and state-sponsored assassinations as carried out by the world's secret services in the name of security? Suddenly all varieties of mitigating issues arise: intolerable suffering, the rights of an individual over their own body versus that same individual's responsibility towards the life which depends upon them, the greater good...
As the waters muddy, so the need for wisdom and compassion increases. Reality has a habit of complicating what we assume is simple. The best way, perhaps the only way, to restore sufficient simplicity to think clearly is to step back, reflect, discuss, pray. And then engage - but in the awareness that one is dealing with real people, some of whom will be approaching the issue with similar care, others who will be reacting instinctively and therefore carelessly. That is why we need more grace!