A 16-year-old child murdered his adoptive parents and his three-year-old brother with a knife while they slept, telling police afterwards he was suffering under school stress, media reports said Monday, according to dpa. The suspect said he snapped under pressure from his parents to perform better at school, police said. The youth used two knives from his father's butchery in the province of Mato Grosso, stabbing his 33-year-old father 13 times and his 43-year-old mother 12 times. The 16-year-old told police the noise from killing his parents woke up the child, whom he also killed after failing to console him. After the bloodbath, he washed himself and the knife he used and went to a party to prepare an alibi. But he later confessed to the deed. The youth was adopted at age 2 by the parents.