A 30-year-old woman, one of the five people injured in the Siam Paragon shooting by a 14-year-old boy on Oct 3, died early on Friday morning, ten days after the incident, according to media reports.
She was the third fatality in the shooting.
In the Oct 3 incident, the 14-year-old boy opened fire with a modified blank gun in the luxury shopping mall in the centre of Bangkok.
The boy had bought the gun via a Facebook page, and on Oct 5 three men were arrested for supplying him the weapon and ammunition. A further three were arrested the following day.
The teenager was brought to the Pathumwan police station for questioning but was in a confused state, saying he had heard voices telling him to shoot people, according to Pol Gen Torsak Sukvimol, the national police chief.
He was admitted to a psychiatric hospital on Oct 6.
Two people were killed in the shooting - a female tourist from China and a female employee at the shopping mall from Myanmar - and five others injured.
One of the injured was Penpiwan Mitthampitak, 30. She was hit two times in the head and two times in the rib cage, and was admitted to the King Chulalongkorn Memorial Hospital for the treatment of serious injuries.
Penpiwan died at about 2am on Friday, after ten days of treatment.
Pol Maj Gen Nakharin Sukhonthawit, commander of the Metropolitan Police Division 6, said there would be no change in legal proceedings against the teen shooter because police investigators have already pressed premeditated murder charges against him.
The investigators would add updated details of the deaths and injuries to their probe report. They would include autopsy results of those who were killed in the shooting in the investigation report, added Pol Maj Gen Nakharin.