Narathorn Sodtiyang, 21, had earlier been charged with assault causing injury.
Huai Khwang police chief Kamphon Rattanapratheep said Narathon would now face the harsher charge of assault causing death after Charoon Maneepan, 82, was pronounced dead at Rajavithi Hospital at 10:50pm yesterday.
The charge was brought against him under Section 290 of the Criminal Code.
Col Kamphon said Narathorn would be summonsed to acknowledge the charge. He did not know when he would report in.
Mr Charoon’s relatives would also be questioned.
On March 14, Narathorn surrendered to Huai Kwang police and admitted assaulting Mr Charoon in a fit of anger.
He claimed the elderly man knocked down his motorcycle with his push-cart tricycle in narrow Soi Chan Muang 2 in Din Daeng area on the evening of March 13 and drove off without offering to assist him.
Narathorn denied reports on social media he was using a mobile phone while riding his bike at the time of the accident, and not paying attention.
He was held in police custody on assault charges.
Mr Charoon was hit with a high, swinging leg kick and then knocked off his tricycle cart to the ground. He was left bedridden and suffered from pressure sores. He was treated at Rajavithi Hospital, but his family later took him home.
Yesterday they took him back to the hospital, suffering from a high fever.
His daughter Nida Maneepan said hospital staff gave Mr Charoon CPR for about 30 minutes after he went into cardiogenic shock, but were unable to resuscitate him.
Doctors said he had a blood infection, she said.
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