Suppose you woke up to discover someone else was "plugged" into you. You didn't agree to this, it just happened. He's a stranger, but otherwise just a regular guy. The trouble is that he is completely dependent on you to survive, if you unplug him, he'll die. If he doesn't bother you at all then it's just weird, you can't unplug him. If his presence is demanding but you can cope if you try then it still seems harsh to unplug him. But surely there is comes a point, before his presence threatens your life where you can justifiably pull the plug, he can't expect you to devote your entire existence and all your resources to keeping him alive can he? I don't know what the answer is but I wouldn't consider it murder.
This thought experiment is for people who think abortion is either murder, or not, ever. It's how I normally think of it but even if you incline to the murder side, things might not be so clear, especially in the case of rape victims.