The Family Crime

There was a family, a father, a mother, a son, a daughter, and a grandmother. One day, they move to another house, the shape of the house was round. Two weeks later they saw their father killed by someone.

The mother said “I was cooking”, the son said “I was doing my Science Experiment homework”, the daughter said “I was shopping in the mall with my friends”,  the grandmother said “I was reading newspaper on the corner”

Who killed the Father?