Sayan Saenoun, the driver who works for Kowit Tharana, a former Democrat MP, appeared on the People's Democratic Reform Committee's rally state in Pathumwan together with another protester who was at the scene of the bomb blast and witnessed the incident.
Mr Sayan said he was driving the pickup truck and following the march led by PDRC secretary general Suthep Thaugsuban when the bomb exploded.
At the time, he said, it was impossible for him to activate the grenade with one hand while the other hand held the vehicle's steering wheel. In addition, he would certainly have died from the powerful grenade blast if he had lobbed it next to his vehicle.
Since then his hearing has been affected from the blast and he will have to meet a doctor again tomorrow for more tests.
Pol Maj Gen Adul Narongsak, deputy chief of the Metropolitan Police Bureau, said the video clips examined by police showed two men acting in a suspicious manner. One of them, wearing a white hat, walked quickly from the tail of the marching column, dropped an object and ran to hide behind a telephone transformer box. After the grenade exploded, the pickup truck driver ran to the iron box and they then came out together to pick up fragments of the bomb and left without paying attention to the people who were injured and lying on the road.