Chatchai Witsayangkul, 23, was arrested for allegedly colluding with his 20-year-old lover to kill his father and his grandmother early Monday morning. His boyfriend, Anuparb Kraithong, was arrested later on the day.

According to a Bangkok Post report, Pichai Witsayangkul, 60, was found dead with multiple knife wounds to the neck, which had also been hit with a 5kg dumbbell in his bedroom at his house in Soi Rambutree, in Phra Nakhon area. His 79-year-old mother, Lamom Witsayangkul, whom police said was strangled to death was found in front of the bathroom.

Chatchai had originally told police that an unknown number of men broke into his house around 2.40am and killed his father and grandmother before escaping with a gold necklace and some 70,000 baht cash. He also claimed to have been injured by one of the assailants who tried to strangle him with a piece of wire.

It was only after hours of interrogation that Chatchai confessed he had killed his father and his grandmother with the help of his boyfriend, whom he had bought to stay with him at his father's house.

Chatchai who was not in the house when the police arrived to investigate had telephoned his mother who was staying at his elder brother's house, and then visited a hospital for a medical check-up.

The suspect who claimed to be a computer engineering graduate said that he was not on good terms with his father and grandmother as they had always scolded him for not trying to find a new job since he quit his job with the Bangkok Mass Transit System Corps.

According to a police investigator, Mr Chatchai claimed that he killed his father because he always used violence against his mother and other family members.