Maj-General Jirapan Bhumijit, commander of the Metropolitan Police’s Division 9, based that assertion on Jan Chaisawas’s autopsy results.

He also said there were no traces of any toxic substance in Jan’s system.

He showed the autopsy results to reporters at the Faculty of Forensic Science at Siriraj Hospital.

Jan’s body was examined there before it was handed over to his family for a religious ceremony later yesterday.

A few days before his death, Jan submitted a petition challenging two orders from the National Council for Peace and Order. The orders cancelled the posts of inquiry officials – a move many believe will pave the way for police reform.

Jan, an investigating officer at Bangkok Thien Thalay Police Station, was found dead at his house on Friday morning after apparently hanging himself.

Jirapan, who was Jan’s supervisor, dismissed a “rumour” spread on social media that the senior investigator had been assaulted before his death. He said Jan had not lost any teeth as had been rumoured.

He added that photos accompanying some social media messages that claimed to show Jan’s bruised body were doctored.

However Kananart Kachana, a senior assistant district chief, said he did not think his close friend had committed suicide and described him as “fun loving”, although he was very serious about his work.

Kananart came with Jan’s family members to claim his body for the religious ceremony.

In a related development the Department of Special Investigation director general, Pol Colonel Paisit Wongmuang, said his agency had no authority to investigate Jan’s death as this case was under the jurisdiction of the Royal Thai Police.

He was responding to Watchara’s request for the DSI to investigate the case.