Pol Col Chaiya Khongsap, chief of the Lumpini police station, said Natthawat Masri, 30, was found dead with his two sons aged 7 and 5 in their house on Phra Jen Road in Lumpini sub-district of Pathumwan district on Sunday morning.
The father was an assistant cook at Banyan Tree Hotel on nearby Sathon Road. The sons were stabbed in the chest and the father had a knife wound also to his chest. A blood-stained knife about 30-centimetres long was found in a bedroom on the second floor of their two-storey house.
Police found a suicide note apparently bearing a message from Mr Natthawat. It read that his wife had gone with another man and he would do whatever it took to keep his children.
Mrs Suwanna Thap-iam, Mr Natthawat's aunt, said the man and his wife had argued a few weeks ago before they separated.
The man brought his sons to the house last Friday and was to send them back to their mother on Sunday evening. At about 4am on Sunday Mrs Suwanna, who lives in the same house, said she heard abnormal sounds from Mr Natthawat's bedroom and later in the morning she found them dead.
In another case, Phisutthinee Wacharasirinant, 40, was stabbed repeatedly in her room at Ratchada Suite Condominium on Ratchadaphisek 36 Road.
She was a director at the Office of Insurance Commission. A colleague found her body in her room on Saturday after she had been absent from work for some days.
Mrs Phisutthinee was seven months pregnant. She was stabbed in the chest, arm and stomach. A knife was found on the floor in the middle of the room.
Pol Lt Sitthiwat Sakharin, an interrogator at Phahon Yothin Police Station, said the woman lived in the condominium with her husband and two daughters. Police suspect the husband of killing her as he and the daughters had been missing from the condominium since June 29.
There were traces of a fight and several cans of beer were scattered around.