A 13-year-old Brazilian boy killed his parents, his grandmother and his great-aunt before spending a full day at school and then taking his own life, police have revealed. The five bodies were found before dawn on Tuesday inside two houses located on the same property in northern Sao Paulo, they said.

"Everything seems to indicate that Marcelo (Pesseghini) killed his parents and relatives," Itagiba Franco, of the Sao Paulo Civilian Police's homicide department, told a press conference.

Police said the teen's parents were killed late Sunday or in the early hours of Monday. Forensic examinations are under way.

Franco said Pesseghini had told a friend he wanted to kill his parents and become a hitman.

"He always told me he wanted to become a hired killer. He had a plan to kill his parents during the night, so that no one would notice and escape in the parents' car and live in an abandoned place," police quoted the unidentified friend as saying.

The teen died from a shot to the left temple and his father's police-issue service revolver was found nearby, Sao Paulo police commander Benedito Roberto Meira said earlier.

A second gun, a 32 caliber revolver, was found inside the backpack the teenager took to school on Monday, Meira added, saying "there was no sign that someone broke into the house".

The police commander ruled out "an act of revenge by a criminal group" against the teenager's father and mother.