The baby sitter the maid the cook and the date

Question: They live in a circle house. A couple and a baby and a cook and a maid. One night the couple asks a babysitter to come watch the baby. The couple leaves for their date. When they return, the baby is dead. So the couple asks each person that was home. Couple to the cook: what were you doing when we were gone? Cook: I was cooking dinner. Couple to babysitter: what were you doing when we were gone? Baby sitter: I was heating up the babies milk. Couple to maid: what were you doing when we were gone? Maid: I was cleaning the corners of the house. Who killed the baby?