Police have launched an investigation after several body parts washed up at different locations in the Chao Phraya River over the weekend.
The parts, including a head and torso, have been sent to the Police Hospital's Institute of Forensic Medicine for DNA testing and identification.
Police say they are awaiting results to determine whether the body parts are from the same person.
A human torso was found Sunday afternoon in the river near Wat Phothongbon in Nonthaburi's Pakkret district.
An hour later a head washed up under a house located by the river in the district.
The head was wrapped in a plastic bag and was emanating a foul smell.
Hours earlier, the lower part of a leg, from the knee to the calf, was discovered by the operator of a long-tailed boat in Nonthaburi's Muang district.
The body part was spotted floating by Wichian Sukto who used a rope to bring it to a pier in front of Wat Tamnak Tai and called the police.
Mr Wichian told police that he also spotted another body part, from the knee to the foot, on Saturday morning and took a picture of it before it was washed away by strong tides.
On Saturday morning, an arm was found by dockyard worker Thanom Mangsachart in Bangkok's Bang Phlat district.
The arm washed up covered in water weeds on the riverbank near Wat Kharuehabodee and was giving off a foul smell.
According to police sources, it is possible the human parts are from the same person, possibly an Asian male.
The condition of the parts indicated they were in the river for about two days.
Uthasin Ritruangdej, commander of the Metropolitan Police Division 7, said he has ordered investigators under his jurisdiction to look into missing person reports and cases, and look for clues about the victim.
The investigation will focus on the past seven days and include the three provinces of Bangkok, Nonthanburi and Samut Prakan, he said.
He said the results of a forensic examination are expected this week and called on those who might have information to contact police to help them in establishing the body's identity.
Pol Lt Col Suphap Phetcharat, an investigator of Borwornmongkol police station in Bang Phlat, said the arm was sent to the Institute of Forensic Medicine for testing and fingerprints would also be taken to see if it matched those of any Thai national.
He said there was a severe wound on the arm suggesting the person could have been tortured.