They are also looking for a former employee of the shop to assist them in their inquiries.

Three women were killed and more than 7.5 kilograms of gold were stolen from the Kim Jia Hua Gold Shop in Samphanthawong District.

The robbery was discovered late on Saturday night when neighbours noticed smoke and the smell of cooking gas coming out of the shop. A neighbour alerted the police after she knocked on the shop's door, rang the bell and shouted without getting any response.

Police and fire fighters arrived at the scene shortly after 11pm and found the shop was locked from the outside.

After breaking open the door and letting the smoke clear, they found three cooking gas cylin?ders left open, one of them already consumed by the fire inside the shop. More than 40 gold necklaces were scattered on the floor along with pieces of broken glass. The shop's safe, about one metre in height, had been cut open and was empty.

The bodies of Jinda Sirapattanakul, 50, her daugh?ter Pawana, 22, and Sunita Maithong, 41, were found on various floors in the shop.

All had severe wounds to their skulls, as though crushed by a hard object.

Sunita was married to Pirom Maithong, the shop's goldsmith and supervisor. She was allowed to stay at the shop because she used to work there before. Jinda worked as a maid while Pawana was a sales assistant.

The shop had stayed closed on Saturday because the owner went to Udon Thani for a merit-making ceremony. Pirom, who has worked at the shop for more than 10 years, was away running some errands in Chon Buri.

Pirom and a shop assistant who had worked there for more than 20 years both suspected that the robbery was done by someone with inside knowledge.

Police said Pornchai sae Kuay told them a woman, a Lao national, was fired by the shop four months ago because she repeatedly stole gold. He said he suspected the 26-year-old woman because the shop had never had any problem with any?one else.

"She often brought her Lao boyfriend to the shop when she worked here," he said. 

Witnesses reported seeing two men carrying a cooking-gas cylinder into the shop at around 1pm on Saturday.

Police Lt-Colonel Songsak Soopanich, an inspector at Chakrawad Police Station, said four false teeth had been found in the shop.

"They apparently belong to a man and they could belong to the attacker. No one in the shop had false teeth," he said.

Jinda's body was found grasping some hair in one hand, and this along with the teeth will be sent for DNA tests, he said.

Police will also check video recordings from the shop's security camera although it might have been switched off on Saturday.

"We will check what occurred in the days before the attack," Songsak said, adding police had also examined footage from a security camera installed by police at a nearby spot.

Metropolitan Police commissioner Lt-General Viroj Chanrangsi said he believed the culprits left the gas cylinders in the hope of causing a blaze that would destroy the evidence and cover up their crime. However, the shop suffered only minor damage from the fire.

"We are investigating this case urgently," he said.

The gold shop's owner Permsiri Wongprakrom, 67, said the victims had worked for her for many decades and usually stayed at the shop. Permsiri lives in a house in Phra Khanong District.