A business dispute could be a motive behind the murder of the owner of a solar cell panel company who was shot dead in Sumut Prakan on Saturday, police said.
Road rage was previously thought to be the motive.
Torphong Tantrawanit, superintendent of Muang Samut Prakan police, said an investigation was looking into the possibility that the death of Akkaranan Monkolchonsawat was the result of a business conflict.
This came after confirmation that a scratch on the front left wheel arch of his sedan was caused a long time ago, according to forensic officials.
Akkaranan's relatives and others in connection with the case have been summoned for questioning, he said.
Pol Col Torphong was speaking after a meeting with the investigation team.
On Saturday, Muang Samut Prakan police and rescue workers were called to an incident in tambon Phraek Sa about 9.30pm.
Upon arrival, they found a driverless white Honda sedan bearing Bangkok licence plates with the engine still running 50 metres from a security guard post in front of the Lally Ville Srinakarin-Teparak Townhome in Soi Mangkorn Nakhee on Theparak Road.
Akkaranan, 56, president of Phoenix World Energy Co, which provides the installation of solar panels, was found lying unconscious on the ground nearby.
He had sustained a bullet wound in his left cheekbone and two others to the chest.
He was taken to Synphaet Hospital where he was subsequently pronounced dead. Police also collected five spent shells from a 11mm pistol found at the scene as evidence.
According to witnesses, a black Honda Civic had followed Akkaranan while he drove along Soi Mangkorn Nakhee to his home on Saturday night. The victim pulled over and got out of his car to talk to an unidentified man aged 30-40 who was the driver of the black sedan.
After a brief quarrel, the man pulled out a gun and shot Akkaranan. He then fled from the scene. No detail was available on what the business dispute might involve.