A Pattaya court on Wednesday sentenced a man, 22, to life imprisonment for murdering two Thai-American boys and a female relative in their home three years ago.

Judge Duangsom Sirichaipatana announced the sentence on Prajak Masawaeng, a native of Kanchanaburi province, after he was found guilty of murdering Michael Liberman, 2, Joseph Liberman, 7, and Wipawee Khamsai, 19, in their house in Bang Lamung district, Chon Buri, at about 4.30am on Jan 11, 2014.

The Pattaya Provincial Court commuted the penalty from death because of Prajak's confession.

Prajak was 19 when he committed the crime. But he had already faced arrest warrants for criminal behaviour, including attempted murder. In January 2014, a police officer who handled the case said the man was a serious threat to society.

"He has a criminal instinct. He poses a huge danger to society. When he drinks, it aggravates his anger. He cannot control his temper and is more likely to commit a crime,'' said Pol Maj Gen Surapol Wiratkosin, then deputy commissioner of the Provincial Police Region 2, who was in charge of the case.

The crime in question took place at a house in the Paradise Hill 2 housing estate on Bunsamphan Road in Bang Lamung district. The deceased young woman was the house owner's niece and the boys were the owner's children.

Prajak went to the house to wait for his girlfriend, who had gone out with the owner of the house, Wilaiwan Liberman, 35.

Ms Wilaiwan was talking to Prajak's girlfriend about getting her a job as a dancer in Pattaya.

Prajak earlier told police he approached Ms Wilaiwan's niece, who was minding the children, and asked her if he could wait inside the house.

The niece, he said, was rude to him. In a fit of rage, he knocked her unconscious and stabbed her and one of the boys to death. When the other boy woke up, Prajak stabbed and killed him too. He then fled the house. 

Some media reported that he was suspected of trying to rape the young woman when the boys awoke to see what was happening.

Prajak had faced arrest warrants for attempted murder, theft and illegal detention in Kanchanaburi. He fled with his girlfriend to Pattaya, where they were later introduced to Ms Wilaiwan.