The crime was not directly linked to the insurgency in the South as officers initially thought.
Investigators on Monday said they had arrested two volunteer rangers attached to the 46th Ranger Regiment in connection with the high-profile murder case. The two - identified as Maming Binmama, 21, Sakuaree Jaesae, 25 - were apprehended on Saturday but police announced their arrest and brought them to a press conference on Monday.
A third suspect and volunteer ranger, whose name was not disclosed, is still at large.
The three rangers are accused of firing war weapons at a house belonging to Jehmu Maman, 40, and his pregnant wife Paleedah Mayu, 33, in tambon Palukasamoh, Bacho district.
The ambush killed the couple’s three sons aged, 11, 9 and 6. Mr Jehmu sustained minor injuries and his wife was shot in the right hand.
Maming allegedly confessed to police that he committed the crime because he believed Mr Jehmu killed his older brother, Abdurrahman, and his pregnant sister-in-law, Rakiyah Sararawor, on Aug 24 last year, said Pol Maj Gen Pattanawut Angkanawin, chief of the Narathiwat police.
Abdurrahman was shot dead after he appeared as a witness in a case relating to the murder of an assistant village chief in Mai Kaen district, Pattani. Mr Jehmu was a suspect in the case but later acquitted due to lack of evidence.
Maming had followed up on the police investigation into his brother’s death, but found officers had made little progress. He then decided to ask Sakuaree and the third suspect to help him take his revenge against Mr Jehmu.
The weapons used in the attack were an M16 assault rifle, an AK-47 and a 9mm pistol.
Pol Maj Gen Pattanawut said an investigation into the killing of Maming’s brother was still underway but it was proceeding slowly because there were no eyewitnesses in the case.
Maming said he committed the crime in a fit of rage and regretted killing Mr Jehmu’s children, adding the case had nothing to do with his unit and was not insurgency-related.
He said a colleague from the 45th Ranger Regiment had borrowed the M16 that he used in the Feb 3 attack and was later shot dead by an unidentified gunman.
The AK-47 used by Sakuaree in the attack was allegedly thrown into the Sai Buri river, while the third ranger suspect is believed to have fled with the 9mm.