The suspect in the murder of former MP Kobkul Nopamorn-bodee who was found poisoned drank the poison voluntarily, according to the results of an official police autopsy released yesterday.

 "There were no signs of choking that could indicate forced-feeding," said Police General Hospital spokesman Maj-General Somyos Deemark.

"He drank the poison slowly," Somyos said.

 The autopsy found no signs of physical struggle and Sa-ngad Phumpheng's teeth and lips showed no signs of force-feeding.

 Sa-ngad was found unconscious on May 31 shortly before police were to apprehend him. He was pronounced dead in a local hospital.

Although Sa-ngad's wife had reported that he had been drinking prior to his death, the autopsy found no alcohol in his blood, Somyos said.

Meanwhile, Royal Thai Police spokesman General Ajiravid Subarnbhesaj said the investigation into the May 27 murder of Kobkul is 80 to 90 per cent complete and could be wrapped up in a few weeks.

Ajiravid said the two men initially implicated as gunmen, Jamron Uamthong and his son Suppharuek, would be questioned to see whether they played other roles in the murder.

The pair were released on bail without charge after providing verifiable alibis.

Police are investigating whether the murder was carried out as a personal favour to an influential figure, rather than in return for money or other benefits, Ajiravid said.

This would make it more difficult for police to link the killers with the person who wanted Kabkul dead, Ajiravid said.

He said police were confident that forensic evidence, especially that collected from the weapons and bullets used in the killing, was sufficient to convict the suspects.

Previously three police teams had worked together on the case, but now - with all suspects arrested and enough evidence to implicate them - it is being handled solely by the Crime Suppression Division to ensure it runs smoothly, Ajiravid said.

Of the six men arrested, including new suspects Winyu Rattanawannee and Wanchana Supachaisirimuang, five had volunteered useful information, Ajiravid said.

 However, Anantsak Srisawas, who allegedly planned the killing, has insisted that he will remain quiet until he testifies in court.

Kobkul died in a hail of bullets while being driven home from a wedding party. She was under police protection after informing local police that she feared for her life.