Murdered on Sunday- Detective Riddle

A man is found murdered on a Sunday morning. His wife calls Detective Mehul, who questions the wife and the staff, and are given the following alibis:

The wife says she was sleeping
The butler said he was cleaning the closet
The gardener was declared he was picking vegetables
The maid explained she was getting the mail
The cook said she was preparing breakfast

Immediately, the police arrest the murderer. Who did it and how did the police know?

• The wife
• The butler
• The gardener
• The maid

The maid