Samut Prakan police said the incident occurred on Theparak road in Bang Phli district.
At the scene, police found a bullet-ridden bronze Honda City parked in the middle of the road. Six people had been in the car and five were wounded -- three men and a woman. All were rushed to nearby hospitals, but two of the men later died.
The investigating officers recovered 35 9mm and .38 bullet cases from the scene.
According to a witness, a 19-year-woman at a nearby karaoke bar, the victims' vehicle was travelling at high speed and was cut off by a black car carrying gunmen who opened fire at it.
After it came to halt, a bronze sport-utility-vehicle stopped next to the car to finish off the passengers at close-range. The SUV left but later made a u-turn and fired at the car again, the witness said. She and her friends got the injured out of the car and then called the police.
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Photos by Suthiwit Chayutworakan
Prinya Permsuk, 19, who later arrived at the scene, told the police that he was the victims' friend. Mr Prinya said they had left his house in Bang Phli district about 30 minutes prior to the shooting.
Montri Wanpetch, 27, an emergency worker, said he happened to be near the scene when the shooting took place and saw four people in the car had been shot.
The injured were identified as Sayan Kaewnuch, 27 who was shot in the left hand and left thigh, and Wannisa Premsri, 27, also shot in the left thigh. They were taken to Bang Phli Hospital and were reported to be in a stable condition.
Veerawat Kwanpetch, 24, suffered multiple gunshot wounds to the body and Apisit Intachai, the driver, who was shot a couple times in his chest, both later died at the hospital.
There was also an unidentified 18-year-old woman in the car who was unscathed. She has already been questioned by the police.
Deputy national police chief Ek Angsananon said after inspecting the crime scene that Veerawat and Apisit had criminal records.
"Both men had criminal records for theft and were involved in the drug business. Veerawat had connections with a major drug dealer in Samut Prakan who was arrested several years ago," Pol Gen Ek said.
Investigators told him the two men liked to visit night entertainment venues and also had arguments with two car tyre businesses, he said.
The Samut Prakan police chief will be in charge of the case, he added.
There appeared to be at least three gunmen carrying out the attack and investigators were reviewing surveillance cameras installed along Theparak road to identify them, he said.
"I believe we'll be able to identify and arrest the attackers soon," the deputy police chief said.