The Runaway Trolley and a Homicidal Doctor

Today I would like to share a thought experiment, and one of its more morally stumping revisions.

Imagine there is a runaway trolley, with no chance of stopping, and tied to the track are five people about to be runover. Luckily a man is stationed at the track switch, however he notices one person is also tied to the other tracks. He now faces the delima of deciding whether to let events place out and let five die, or switch the tracks and killing one.

So what should he do? If you found the question easy, allow me to propose another.

A doctor has five patients with different failing organs. All of them with the same rare blood type, they will die before a donation comes along. However the doctor remembers an ex-patient of his who would be a perfect match, and contemplates killing him in order to harvest his organs. He now finds himself in the same dilemma as the track switcher even if different circumstances.

So what should they do, kill one to save five, or let events play out how they will? If you came up with different answers to each scenario, I would love to hear why.