I can more likely see Ben dragging Penny to the island somehow (time travel/submarine/airplane/helicopter/motorcycle/smokey/whatever) and having Locke kill Penny through some method of manipulation.

Locke could'nt even kill his dad, unless something really crazy happens(which is almost everyweek) I dont think Locke could kill Penny after knowing Desmond as well as he does..

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what are you guy's talking about,who's your favorite other
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Sawyer