Forensic results will today show which vehicle fired the first shot during the road-rage drama two weeks ago in Khao Yai that killed an MP's son, police said yesterday. About 70 per cent of the evidence to draw a conclusion had been collected, Pol Col Bunsong Attaworranant said yesterday.

Mun Phoolsab, 40, who surrendered on Thursday, and four passengers in the SUV driven by Farut Thaiset, the son of Chart Thai Pattana Party MP Chada, have claimed the other side opened fire first.

Police may need to perform a post-mortem on Farut, with approval from Chada, to seek extra trajectory details.

Mun told police that while he was driving his pickup, he returned fire with three shots at the SUV, but Farut took one fatal shot to his left temple and the SUV showed one bullet hole, Bunsong said.

Besides who shot first, police are also working on two other critical questions - if there was another person in Mun's pickup, as the four SUV passengers have insisted, and where Mun's handgun was.

The suspect, a construction contractor from Ratchaburi, said he threw it a long way from the scene in Nakhon Ratchasima's Pak Chong district. He has been charged with premeditated murder, possessing and carrying a handgun and ammunition without a permit and discharging a firearm without good cause.

Police have not found the murder weapon despite a thorough search of the area where Mun said he disposed of it, so Mun will be questioned again today.

Chada's attorney Suppharuek Iamla-or said exhuming Farut's corpse was "extremely difficult" because it was against Farut's Muslim religion. "If police insist on the autopsy, talks between the officers and the Thaiset family will be held to discuss the issue. Personally I think the autopsy is not needed as the suspect has admitted to shooting at the SUV," he said.

Police only needed to recover the murder weapon, he said. Neither he nor the Thaiset family was informed of a possibly autopsy on Farut's body, he said.

A police source, citing crime scene results, said spent cartridges from guns carried by the SUV occupants were found first along the stretch of road where both vehicles were travelling together, while a cartridge fired from the supposed handgun of Mun was found where the SUV tipped over and rammed a pole.

"The first spent cartridges should signify that people in the SUV opened fire, and the last cartridge should signify that the suspect was the last to shoot."