Circular Mansion Riddle

In a circular mansion, a man has been discovered dead. Detective Mehul examines the babysitter, maid, and cook.

The cook claimed he was too busy preparing the food to have been able to do it.
The maid claimed that she was engaged in cleaning the corners to have done it.
The babysitter said she couldn't because she was playing with the children. 

Who's the liar? How did Detective Mehul discover?

• The maid
• The Babysitter
• The Cook
• None of them

The maid