The Family Crime

There was a family,a father,a mother,a son,a daughter,and a grandmother.Then one day,they move to another house,the shape of the house was round.Then 2 weeks later they saw their father killed by someone.the mother said “I was cooking.”, then the son said “I was doing my Science Experiment homework.”,then the daughter said “I was with my friends shopping in the mall.”,then the grandmother said “So it will be silent I went to the corner reading newspapers.”

Who killed the Father?