His efforts helped police find the suspected murderer and eventually catch him.
Veerapong Chomruk, 30, was riding a motorcycle on his way to work at a bank yesterday morning when he saw a car come to a sudden stop on Praditmanootham Road in Lat Phrao district.
A woman, later identified as Phuangpaka Ruthawanit, 58, fled the vehicle with a man in hot pursuit.
Mr Veeraong, who witnessed the incident, said the man caught Phuangpaka and stabbed her with a knife.
Police and rescue workers later confirmed she died before being sent to hospital.
An examination of her body found a total of 13 stab wounds.
The alleged killer, later identified as Rewat Ngamboonplod, 32, then used the knife in the theft of a pickup truck that was parked nearby and fled the scene.
Mr Veerapong, now being praised for his good Samaritan actions, decided to pursue the fleeing suspect.
"The first thing which entered my mind was that I should help catch the wrongdoer so I drove after him and called Jor Sor 100 radio station.
"I told the traffic radio station what I had seen. After that, police kept contact with me along the way," Mr Veerapong said after the pursuit.
Police from Chokechai station arrived at the murder scene about 9.30am, and took up the pursuit of the suspected killer based on Mr Veerapong's information.
With the motorcyclist's help, the officers stopped the vehicle in tambon Wang Takian of Chachoengsao's Muang district, about 80km from the crime scene. "I was afraid he would see me so I kept a safe distance from him," Mr Veerapong said.
He also admitted he was about to run out of petrol by the time the police caught up with the suspect.
"If he had gone further, I could not have followed," he said.
He asked passersby to help follow the man but none of them did.
"I do not blame them. I believe everyone is kind, at least in mind. The people I asked probably did not realise what was going on," said the father of two young children.
Mr Veerapong said his wife also asked him why he had taken the risk of following a suspected killer.
"It's not that I wasn't scared, but I told her I couldn't turn a blind eye. If the situation was reversed and we ended up the victim, we would want other people to help us," he said.
Police said Mr Rewat admitted stabbing the woman, his boss. He said she had been scolding him while they were travelling in the car. A heated argument erupted, she fled and he chased and attacked her.
Afterwards, Mr Rewat allegedly said he had thrown the knife into a pond on the side of Suvinthawaong Road.