Let's see how smart we are

A man was found murdered on 14-10-2015 Sunday afternoon inside his house.

His wife called the police and they asked everyone around a question.

Police: Where were you when his death happened?

WIFE: I was sleeping upstairs when the murder took place

COOK: I was cooking in the kitchen

HOUSE GIRL: I went to collect the children from school.

GARDENER: I was cutting the flowers at the backyard.

GATE MAN: Oga sent me to buy newspaper for junction. After listening to their answers, the police arrested the murderer.

Who was the murderer??