Police found the body of the 48-year-old executive in her bedroom on the second floor of her condominium on Narathiwat Ratchanakarin 7 Road (Phra Phinit Road) in Sathon district, Bangkok.
The body of her 54-year-old husband Reto Castellazzi was also found nearby with a gunshot wound to the face and an 11mm gun in his hand.
The police found 11mm bullets in front of the condominium building and in its parking area where a pickup truck was also shot. Three 11mm pistols were found in their room.
Watcharin Sukthongsa, a 45-year-old security guard chief of the condominium, said that he drove his truck to the place at about 8pm and a bullet suddenly hit it. Then he saw the Swiss man firing several rounds on the balcony of the couple's suite.
Mrs Ngad, the couple's maid, said the couple had just returned from an exercise and had been having a meal. At the time of the shooting, she was ironing clothes.
Pol Maj Gen Suebsak Phansura, commander of the Metropolitan Police Division 5, said the Swiss man had worked as a computer engineer and later resigned for mental illness. He was on medication.
The police initially assumed a domestic conflict caused the tragedy and the husband might have lost temper and killed his wife and then himself.
The couple had a 14-year-old daughter who was not home at the time of the murder.
Mrs Kritaya was a cousin of Nualphan Lamsam, the president and CEO of Muang Thai Insurance Plc and manager of Thailand's female national football team.
Mrs Kritaya was a daughter of Yutti Lamsam, vice-chairman of Muang Thai Insurance, and Mrs Kosal. A graduate from Chulalongkorn University's Commerce and Accountancy Faculty, she finished her master's degree from Boston University in the United States.
Later on Saturday Mrs Nualphan said relatives were saddened but had always been aware of Mr Castellazzi's mental problem.
She did not know if the couple had had conflicts but expected Mr Castellazzi's relatives in Switzerland to pick up his body for a funeral after his autopsy.
Pol Maj Gen Thitirat Nonghanpitak, deputy commissioner of the Metropolitan Police Bureau, said the police were checking information about the three pistols at the condominium and waiting for forensic examination.
He said the condominium was heavily guarded and it was difficult for strangers to enter the compound.
Pol Col Kittipong Suwan, chief of the local Thung Mahamek police station, said that security camera footage showed that no outsiders entered the condominium during the time of the crime.
As Mr Castellazzi had been treated at a hospital on La Salle Road in Bangkok, investigators gave more weight to domestic fights and the theory was that the man killed his wife before turning the gun on himself.
However, investigators had not ruled out other possibilities including murder and suicide, Pol Maj Gen Thitirat said.