Two Massachusetts girls and the brother who stabbed them to death are being mourned at a single funeral service.

Family and friends gathered Saturday morning at the Jubilee Christian Church in Boston's Mattapan neighborhood for a funeral for the siblings.

A week ago, 17-year-old Samantha Revelus and her 5-year-old sister, Bianca, were killed at their home in Milton.

Police burst into the apartment and saw the girls' brother, 23-year-old Kerby Revelus, decapitating Bianca with a kitchen knife.

Police say they shot Kerby Revelus dead as he tried to attack another sister.

A spokesman for the children's parents said they are "in shock and disbelief" and have no explanation why their son would kill his sisters.