guess who??????????

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A man was found murdered on sunday morning. his wife immediately called the police. the police questioned the wife and staff and got these alibis.. the wife said she's sleeping the cook was cooking breakfast the gardener was picking vegetables outside the maid was in the post office mailing letters the buttler said he was cleaning the closet upstair after that the police arrested the suspect immediately who is the murderer and how did he found out????? post your answer and why?????????