Massachusetts ? A man fatally stabbed his 17-year-old sister, decapitated his 5-year-old sister in front of a police officer and then turned toward his 9-year-old sister with a knife in his hand before officers shot him dead in what their chief described as “a killing field.”

There was no clear motive for the events that unfolded Saturday, the day after the 5-year-old’s birthday, in a tony Boston suburb that also is home to Gov. Deval Patrick. But there was no doubt about the carnage wrought by 23-year-old Kerby Revelus against his sisters in the two-family home they shared with their parents and grandmother.

Five-year-old Bianca was killed as a cake for her birthday, which investigators believe was Friday, sat on the kitchen table. Nine-year-old Sarafina dialed 911 and watched police shoot her brother as her elder sister, 17-year-old Samantha, lay dead on the floor.

Sarafina was hospitalized Sunday with defensive wounds to her hands and stab wounds in her abdomen and one of her legs, police said.