a man was found murdered on early Sunday morning. his wife immediately called the police. they interviewed the wife and staff and got these alibis.

the wife said she was sleeping.

the cook was cooking breakfast.

the gardener was out picking vegetables.

the maid was getting the post.

and the butler was cleaning the closet.

the police instantly arrested the murderer. who is it and how did they find out?

hint: the answer is not a certain character but it has to do with the first book. read carefully!