A man and a woman were driving in their car when it broke down. The man decided to go for help at a gas station a few miles back. He made sure nobody was in the car, rolled all the windows up, and locked all of the sedan's doors. He went off, but when he came back, his wife was dead, and there was a stranger in the car. No physical damage was done to the car, so how did the stranger get in?
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Your question doesn't really seem to pertain to any study-group.
He either made a calculation in story when, A. he didn't really lock the doors, or B. the person was already in the car.
We could also assume that, if all was true, that would violate natural laws and become a paradox. However, this is not possible. His wife must have unlocked the doors to come in after him, or step out of the car for a moment. When this happened, the stranger attacked her. The woman might have saw the stranger first, and in panic, tried to run, but he chased her down.
The information is too vague in order to give an absolute answer, but I feel these are the best solutions.
She was most likely pregnant, gave birth when the man was gone and died giving birth to the baby? :I
The baby would be a stranger since the man had not seen the birth taking place, so the baby was alien to him. That would be the only logical reason (riddle wise) since the windows and doors were locked-shut and the women could not simply let anyone in.