The source said the DSI had found that most of the 11 special cases related to the "war on drugs" that it was reviewing had been recorded by the police as "silence" killings among drug-dealing networks and thus their investigations into these cases ended with no culprits brought to justice.

"In the Chakraphan case, it was found that police caused the boy's death and a murder charge will be filed soon against those involved. As for the police officers who together produced a faulty case report, the DSI will seek an NCCC [National Counter Corruption Commission] probe against them for abuse of authority," the source said.

On February 23, 2003, Chakraphan and his mother Pornwipa were waiting in a car while the boy's father allegedly went to deliver illicit drugs to an undercover police officer in a sting operation by police in Bangkok Bang Chan area.

Police allegedly riddled the car with bullets when Pornwipa spotted them and tried to drive away. Chakraphan was killed instantly while Pornwipa fled the scene and has not been seen since.

Speaking about the Royal Thai Police's own probes into some 2,500 alleged "silence" killings during the notorious "war on drugs" launched by the Thaksin government in 2003, DSI director-general Sunai Manomaiudom said the police were authorised to investigate the deaths, but could not interfere in or investigate the 11 cases covered by the Committee of Special Cases.

Sunai said he did not want the public to think the DSI and the police were competing.

Deputy police chief Lt-General Jongrak Juthanont, who heads the force's probe into killings during the war on drugs, said police were examining all files related to the crackdown to get wrongdoers punished "without exception".