The incident took place at a two-storey home in Mela Vill housing estate in Thanyaburi district of Pathum Thani at about 3am Sunday, Pol Col Trakoon Kiawpraserty, chief of Pratunam Chulalongkorn police station, said on Sunday.
The boy’s father, 44, worked as a government official, while his wife, 41, owned a clothing business.
They were sleeping in their bedroom on the second floor of the house when their younger son, whose name was not given by police because he is a juvenile, apparently took his father’s Glock pistol from a closet and shot both in the head. The youth's body was found lying face up on the ground by the foot of the bed with a gunshot wound to the head and the gun nearby, Pol Col Trakoon said.
The teen's 19-year-old brother, whose bedroom is downstairs, told police the youth usually slept in his parents’ room. That night he heard a few loud bangs but did not suspect anything and went back to sleep. He went to his university in the morning, returned home in the afternoon and found no one around and the family's two cars still parked. He then ran to check his parents’ room and found it was locked with the air conditioner turned on.
He broke open the door and found the bodies of the three inside.
He believed his brother, who had just completed grade 10, killed his parents after they rebuked him for making poor grades at school. They had seized his smart phone so he would pay more attention to his studies than games.
The couple also grounded the youth from driving the family cars.
His brother told police the teenager may have felt under extreme pressure or was sulking because of his parents' strictness.
Pol Col Trakoon said he had instructed investigators to examine gunshot residue on the youth's brother's hands.