A 30-year-old man stabbed his father to death inside their Brooklyn apartment before attacking his sister and then jumping out the window to his death early Tuesday morning, police said.

Kostyantyn Proskurnyak allegedly attacked his father, Voclodymyr Yeushchenko, just after 2:30 a.m. Proskurnyak fatally stabbed the older man in the neck inside the Brighton Beach apartment they shared, police said.

But when Proskurnyak's 29-year-old sister walked in, he attacked her too, stabbing her back, wrist and forehead before she ran.

The woman, who was not identified, was found on the corner of Coney Island and Brighton Beach avenues, about three blocks away from the apartment, police said.

Proskurnyak then jumped out of the second floor window, police said. His body was found alongside the building with severe trauma and he was taken to Coney Island Hospital where he was pronounced dead.

It was not immediately clear why he attacked his family.

Proskurnyak's sister was taken to Lutheran Medical Center in stable condition, police said.