The school headmaster who admits robbing a gold shop in Lop Buri province and shooting seven people said he did not mean to kill the two-year-old boy or a woman employee, but police will press charges of premeditated murder.

Prasittichai Khaokaew, 38, answered reporters' questions via an audio link to a press conference at the Royal Thai Police headquarters in Bangkok.

He said he intended to shoot a security guard at the Robinson department store in Lop Buri province where he robbed gold shop, and the bullet hit the boy by accident. 

"I ...[pause]... did not see the child. I shot the security guard to clear the way. I didn't mean to shoot the child. I regret that," Mr Prasittichai said.

Two-year-old Titan was killed as he walked past the Aurora gold shop with his mother when the robber stormed up to the display counter about 8.44pm on Jan 9.

Security camera footage shows the robber shooting at gold shop staff and customers. A woman employee was also killed and he shot dead a security guard as he escaped.

"I shot to ...[pause]... clear the way and trigger fear," Mr Prasittichai said.

He claimed that his gloved finger stuck on the trigger of his gun, and caused him to accidentally shoot dead the gold shop employee.

After he shot the woman his instinct told him to continue shooting at the customers, and he regretted that,  the headmaster of Wat Pho Chai School in Sing Buri province said.

The suspect also said that he bought the sound suppressor attached to his pistol from a young friend he knew on the net.

"I wanted to soften the noise because I did not want to frighten people," Mr Prasittichai said.

Although he used his father's gun and his father-in-law's motorcycle during the crime, he was adamant that he acted alone. He had intended to surrender on Friday, after finishing some work he had to do for his pupils, the suspect said. Instead, police arrested him in Lop Buri as he drove to work on Wednesday morning.

Repeatedly asked about the motive for the crime, Mr Prasittichai said he had personal and financial problems. He refused to elaborate, and asked police to end the question and answer session. 

Police earlier said the suspect would be flown back to Lop Buri for a crime re-enactment. However, this was cancelled.

There was no suggestion of bail.