Riddle of the day and Harry Potter.

So! I love riddles, I always have. I decided to post this riddle I found and YOU can see if you can figure out the answer.

A man was found murdered on a Sunday morning. His wife immediatly called the police. The police questioned the wife and the staff and got these alibies:
The wife said she was sleeping.
The cook was cooking breakfast.
The gardener was picking vegetables.
The maid was getting the post.
The butler was cleaning the closet.
The police instantly arrested the murderer. Who did it, and how did they know?


SPOILER!!

Originally I thought it was the wife, because if she was alseep how did she immediatly call the police? But then I figured someone woke her up...


HINT!!
Anyone who has seen the first Harry Potter movie should kind of have an idea... Think of Uncle Vernon.