Who's the Murderer?

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Guys try this one. One sunday morning, a man found dead on his house. Soon the police came and ask the people living with him. Here are the alibis: wife: when I woke up, I found him dead! Cook: I was cooking in the kitchen, I didn't notice. Maid: I was in the post office mailing letters. Butler: I was in the roof that time. Gardener: I'm planting outside. After hearing all there alibis, the police caught the killer. Now, can you figure out whose the killer?