CCTV footage from the Robinson mall in Lopburi province, about 145 kilometers (90 miles) north of Bangkok, shows the man carrying a pistol with a long silencer approaching a counter around 8 p.m. Thursday and shooting a seller and another victim before jumping on the counter and snatching trays of gold necklaces.
The regional police commander, Lt. Gen. Ampol Buaruppon, told reporters the man came into the mall alone and opened fire at a security guard who he came across and then started a shooting spree that killed three people and wounded another four.
"The robber was merciless. We are looking for him in every place. Please trust us, we will definitely get this man and bring him to justice," he said, adding police were authorized to use lethal force if he resists arrest.
Police also offered 100,000 baht ($3,300) for information leading to the gunman's arrest.
The parents of the 2 year-old who died in the shooting posted a message on their Facebook page, saying "We love you very much. We are so sorry that we cannot protect you … Rest in peace our angel."