"The driver had an acute stroke while on the wheel and lost control of herself," acting Bangkok police chief Pol Lt Gen Sanit Mahataworn said.
"Her daughter, who was with her in the car, told us her mother suddenly had a seizure and lost control of the car before it hit the shrine," he said, adding that a DNA test also showed it was the mother who was behind the wheel.
An explosive device was hurled at Sathorn pier the very next day but caused no injuries or damage as it bounced into the water and exploded there.
In yesterday's incident, the CCTV footage showed the car was in reverse gear after the hit but that was because the daughter was pulling the gear lever or the impact could have been much greater, the police general was quoted as saying by the Bangkok Post.
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Local media reports put the number of injured persons, who were paying respects to the Hindu god at the shrine, to six and identified them as nationals of Indonesian, Singapore and China.
They are hospitalised but now safe, the reports said.
Mahataworn said the doctor who conducted dyed CT scanning on the driver told the police she did have a stroke. In the meantime, the police might have to press charges until the official confirmation comes.
"If the doctor officially confirms the driver could not possibly have controlled the car in such a condition, she will not be held criminally responsible but civil charges might be filed by the victims," he said.