Saraburi police are questioning the former boyfriends of Klinkaysorn Wongsing, a 36-year-old sales representative and restaurant owner who went missing in November 2016, after her remains were discovered in a car retrieved from a canal in Nong Don district on Monday.
Among the "persons of interest" in the case are a fellow fertiliser-sales rep who lives in Samut Prakan and an older man who provided financial support for Klinkaysorn's steak restaurant and costume rental business, Pol Lt Col Natthawara Kanthayot, chief investigator at Nong Don police station, told media on Tuesday.
The victim's former husband is among those helping police with their inquiries, he added.
However, just before she disappeared, Klinkaysorn had lodged a complaint at Bang Rachan police station in Sing Buri accusing her ex-husband of trying to assault her.
Saraburi police have so far questioned the victim's mother and another relative.
The next person to be interrogated is Klinkaysorn's sister and the four eyewitnesses who spotted the car in the Nam Chai Nat-Pasak canal.
The case is back in the spotlight after the car and its gruesome cargo were pulled from the canal on Monday.
Villagers discovered the car lying on its roof at the bottom of the canal in tambon Nong Pong, after it was drained to irrigate rice fields during the dry season.
It took three hours to hoist the vehicle out of the canal, and inside rescuers found badly decomposed human remains wrapped in a bed sheet.
The remains were later identified as those of Klinkaysorn by her mother Lanthom Wongsin, 56, who lives in Lop Buri.
Police believe Klinkaysorn was murdered because the body had been wrapped in the bed sheet.
They have also launched a forensic examination to officially confirm who the remains belong to.
The victim's relatives told investigators that Klinkaysorn was seeing an older man who owned a fertiliser business in Phra Phutthabat district and had spent the night with him in his office before disappearing three years ago.
Police are examining the remains of the body and other items found in the car, but say uncovering any clues will be very difficult because the evidence has been buried in mud for three years now.