A teenage boy who was obsessed with the Amityville killings shot his entire family, went to school and then returned home and killed himself.
Marcelo Pesseghini, 13, drove his mother's car to his school in the early hours of Monday morning, apparently after murdering his father and mother - who were both police officers - and his grandma and grand-aunt.
He then spent the night in the car, went to school as normal and got a lift home from a friend's father afterwards.
When the friend's dad went to ring the intercom of Pesseghini's apartment, the boy told him his father was sleeping and let himself in instead.
His police sergeant dad Luiz Pesseghini, 40, was found dead in bed.
Mum Andreia Pesseghini, 30, a military police officer, was found on her knees in the bedroom.
Grandmother Benedita de Oliveira Bovo, 65, and great-aunt Bernadete Oliveira da Silva, 55, were both killed in bed in a different area of the house where they lived.
The schoolboy was found dead with a gunshot wound to the head. His dad's police-issue service revolver was found nearby.
Inside a backpack Pesseghini took to school was found a second gun - a .32 caliber revolver.
Police believe Marcelo was carrying out a chilling re-enactment of the Amityville family massacre where a man shot dead his parents, two bothers and two sisters in their beds at home in Amityville, Long Island, New York.
The schoolboy posted a picture linked to the infamous 1974 killing spree on his Facebook page eight months ago.
The incident has shocked people in the Brazilian city of Sao Paulo. Initial indications are that the boy took the weapon he used from his parents.
Police said Marcelo, who was also obsessed with the video game Assassin's Creed, had told a pal that he wanted to run away from home and become a 'hired gun'.
Detective Itagiba Franco said: "This friend told us 'he was always urging me to run away from home and become a hired killer'.
"He had the plan to kill his parents during the night, when nobody would notice, and flee in his parents' car and live in an abandoned building'."