Parents have let the mental treatment institute where he was detained continue treating their 14-year-old son who killed three people on a shooting rampage at Siam Paragon mall in October.
Siriprakai Worapreecha, deputy director-general of the Department of Juvenile Observation and Protection, was quoted by media as saying that the department's authority to detain the boy ended on Sunday, but the parents agreed to keep him in psychological treament at the Galya Rajanagarindra Institute.
Prayut Pecharakhun, spokesman for the Office of the Attorney-General (OAG), said on Monday that police could not submit their reviewed investigative report to public prosecutors by Sunday evening, the deadline for the boy's continued detention.
Doctors concluded that the boy was mentally ill and needed continued treatment so that he would recover and not be harmful to society, Mr Prayut said.
Prosecutors earlier returned to police a summary of their investigation into the Siam Paragon shooting, noting it lacks a sufficiently clear mental health assessment of the teenager.
The boy allegedly carried out the shooting rampage inside the popular shopping complex, Siam Paragon, on Oct 3. One Thai and two foreign nationals – one from China and the other from Myanmar – died in the attack. Four others, including a Chinese tourist and a Lao worker, were wounded.
After reviewing the summary, prosecutors found the police had concluded their report prematurely before receiving the boy's mental health assessment.
Pathumwan police submitted the summary on Dec 20. It outlined the charges, including premeditated murder, possession of a firearm, and bringing and using a firearm and ammunition to a public place without permission.
According to the OAG's Youth and Families Division 3, the police took the suspect to the Galya Rajanagarindra Institute to undergo psychiatric rehabilitation, based on the belief he was suffering from a mental illness.
Yet they proceeded to press charges on Nov 3 despite the institute not having released its assessment. They also failed to discuss the shooter's mental condition with doctors beforehand.
Released on Nov 21, the assessment suggested the suspect was unable to understand the charges, communicate effectively or control his emotions.