Three more suspects have been arrested in connection with the murder of a 16-year-old maid whose body was buried in Phetchaburi five years ago.
They were identified as Pramote Suwanphithak, aka Phu Yai Boy, 43; Panatda Suwanphithak, 21; and Pratthana Thuamsap, 35.
Mr Pramote is the younger brother of Krisana Suwanphithak, the accused who was detained earlier for allegedly killing her maid Jariya "Nong Nam" Srisak and burying the girl's body in the province five years ago.
Ms Panatda is Ms Krisana's daughter, and Ms Pratthana is her personal assistant.
The two relatives of Ms Krisana were apprehended in Muang district of Phetchaburi Monday morning while Ms Pratthana was detained on Sunday night in Phuket.
They have been charged with colluding to help others escape punishment, police said.
Arrest warrants were sought for the three after Ms Krisana implicated them in the crime.
She told investigators Ms Pratthana colluded with her to beat Jariya to death and helped her conceal the girl's body.
The investigation also found Mr Pramote was a village head where the body was buried, and Ms Krisana daughter helped her conceal the body.
The warrant for Ms Panatda's arrest was issued by the Phetchaburi Juvenile and Family Court as she was 16 years old when the incident took place. The suspects were brought to a police news conference at the Crime Suppression Division (CSD) on Monday, after they were arrested and processed.
Phumin Phumphanmuang, chief of the CSD's Division 5, said all of them admitted they colluded in destroying and concealing Jariya's body at Ms Krisana's mother's house in Ban Na Mon in tambon Nong Sano, Muang district in April, 2012.
Pol Col Phumin said the charge of colluding to help others escape punishment had a 10-year statute of limitations.
However, a charge police wanted to press of concealing and destroying a body expired in April as its statute of limitation was five years.
The trio were taken to the Criminal Court where police submitted a request for the first period of detention.
On Sunday, the police department's Institute of Forensic Science (IFS) revealed results of a forensic test that showed DNA recovered from the skeleton found buried at Ms Krisana's mother's home matched Jariya's.
The case came to light after Jariya's mother, Janthira Srisak, 48, told the Central Investigation Bureau (CIB) that she had been told that her daughter had been killed and the body was buried there.
She travelled from Phetchaburi to Bangkok to seek help from the Pavena Foundation after receiving the information from an unidentified witness last month about her daughter who had been missing for five years.
The foundation helped her lodge a complaint with CIB chief Pol Lt Gen Thitiraj Nhongharnpitak who promptly ordered a probe into the case.
The police raided Krisana's mother's Phetchaburi house and found the skeleton, which was taken to the IFS in Bangkok for examination.