The possible answers are direct opposites: CAN'T HAVE BEEN means you believe it wasn't her, while MUST HAVE BEEN means you are sure she was the murderer. CAN HAVE BEEN and MUSTN'T HAVE BEEN do not exist!
Explanation
The two possible answers have different meanings: COULDN'T HAVE TAKEN implies that he would have done it, while MIGHT HAVE TAKEN keeps an element of doubt.
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