Police have been kept on their toes in the investigation into a wealthy criminal suspect who has been given the alias "Ice Metal Casket".

Apichai: Arrested on suspicion of multiple murders. police photo

Investigators suspect Apichai Ongwisit, 40, was involved in the murders of at least three women and believe he used metal caskets in which he tortured his victims to death before concealing their corpses in different locations at his property.

The interrogation of a former security guard at Apichai's house led police into the realms of the macabre when they found more than 300 human bone fragments in the 20-rai compound in Bang Kae district of Bangkok.

Apichai was arrested last month after police found the body of Warinthorn "Kuk-kik" Chaiyachet, 22, from Sakon Nakhon, wrapped in a plastic bag and buried on the man's property at the end of Soi Phetkasem 47.

As the investigation proceeded, police stumbled upon many bones in the pond. Metropolitan Police Bureau chief Pol Lt Gen Pakkapong Pongpetra said the evidence suggests there have been at least three victims, Warinthorn and two other females, one of whom is believed to have been between 15-18, and the other an adult.

He said police are looking into a large number of missing person complaints which may help them identify the other two dead women.

As the bones in the pond are key evidence for pressing additional charges of murder against Apichai, who has already been accused of abusing drugs, illegally possessing a gun and concealing dead bodies, police are focusing on accounts from the suspect's former security guard.

Late last year, Chaloemchon Ngabua, 41, told police of his connection to Apichai in an attempt to secure leniency for a drug offence.

Chaloemchon said he and Apichai had spent time in prison back in 2012 and after they were released, Apichai employed him as a security guard at his house.

During his time there, he claimed Apichai had a heated argument with Warinthorn before hitting her with a stick and stuffing her inside a metal casket for two days, until she died of suffocation. Chaloemchon said the body was then placed in a large plastic bag and buried in the backyard.

Police said the woman's body was identified by her family who recognised a fish tattoo on her back. "Police listened to [Chaloemchon's] statements despite them being the words of a khi ya [drug addict]," Pol Col Jirakrit Jarunpat, chief of city police Women's and Children's Welfare Division, told the Bangkok Post.

His investigation team then spent days looking into the backgrounds of Apichai and his father. They also questioned women who claimed they had been forcefully detained by Apichai in the past.

On Jan 9, police raided Apichai's house and nabbed him, along with drugs and a gun. They also searched for the female victim who Chaloemchon had told them about.

The officers found Warinthorn's body buried in the garden and wrapped in a plastic bag.

According to investigators, Warinthorn had worked as a "sideline woman" who entertained guests at bars. At one of the bars, she met Apichai with whom she entered into a drug-fuelled relationship. She had later lived together with him at his house prior to the discovery of her body.

The Warinthorn case prompted police to expand their investigation and conduct a forensic search of Apichai's house and grounds.

On Jan 16, a team of divers retrieved 28 pieces of human ribs and hair from the pond believed to belong to a girl aged between 17 and 18. The next day, police found another 288 pieces of human bones wrapped up and weighed down by heavy dumbbells in the pond.

On Jan 23, 30 more pieces of human bones were discovered in the pond, this time in a casket. Initial findings suggest they are probably female bones.

These findings led police to the conclusion that at least three women, including Warinthorn, might have fallen prey.

Experts at Siriraj Hospital's forensic medicine unit are testing to see whether the bones match people declared as missing in police files.

"But this is a difficult case," Pol Col Jirakrit said, as the probe into the second and third corpses requires a detailed analysis of data going back many years.

Even in the case of Warinthorn, the suspect has flatly denied he killed her and claims she died of a drug overdose.

Apichai is the son of Chaloemchai Ongwisit, who ran the now-defunct Ongwisit market. His father was also arrested in 1983 for killing an underage girl in anger after she broke his fish tank.

He concealed the corpse by cutting up her body and scattering the parts in many locations. Chaloemchai was shot dead after his release from prison.