Justice Minister Somsak Thepsutin expects to take one more month to more closely link a suspect to the murder of a Japanese woman in Sukhothai after lab tests found DNA of the suspect's relatives match genetic traces on the victim's clothes.
The investigation, which has dragged on for 12 years, must culminate with a final answer though a man believed to have killed Tomoko Kawashita has died and the DNA samples collected from Kawashita's trousers are not perfectly complete.
"We can't close the case today but we'll go as far as we can," Mr Somsak said yesterday, looking forward to confirming whether the man in question really stabbed the Japanese traveller to death in Sukhothai Historical Park in 2007.
The murder suspect, whose name was not revealed, has come under the spotlight after his friend told officers the man claimed he attacked Kawashita with a knife during a drinking session. He was later poisoned in 2010, according to investigators.
The Department of Special Investigation (DSI), which is handling the case, could not collect his DNA for examination because his body had been cremated.
However, Mr Somsak said, the analysis of DNA samples given by his two older sisters, aged 48 and 46, and his son, gave the DSI new hope.
"A lab result found DNA of his second sister matches that on the victim's trousers," the minister said. His first sister and the 17-year-old son equally have seven matching positions of DNA.
This will pave the way for further investigation as experts prepare to examine chromosomes that make up the DNA of the suspect's father, Mr Somsak said.
So far they have conducted DNA tests on 330 people for comparison with genetic carriers found on Kawashita's clothes. "The Thai government has never abandoned this case," Mr Somsak said, adding Japanese authorities could join the probe if they want.
"But if eventually we can't find that final answer, I have to apologise for wasting money," he said.
Kawashita, 27, arrived as a solo traveller in Thailand and visited Sukhothai for the Loy Krathong festival on Nov 24, 2007.
She was found dead near Wat Saphan Hin in Muang district the following day.
The DSI took over the case in 2013 after local police failed to make progress. Mr Somsak earlier expressed concern over the impact on local tourism as fewer Japanese people have visited Sukhothai since the incident and Thailand would like to give them the confidence to come back.