IGP Naving Payeng said the Capital district Superintendent of Police had received the report of Pul's viscera test from the Guwahati-based forensic science laboratory last week.
"There are 99 per cent chances that he committed suicide," state DGP S Nithiyanandam told PTI.
The 47-year-old leader's body was found hanging in the official Chief Minister bungalow here on August 9, less than a month after he had to quit as Chief Minister following the July 13 Supreme Court verdict.
Denying that he had given any press statement ruling out foul play in his death, Mr Payeng said the report did not find presence of any poisonous evidence and confirmed it was a case of suicide.
However, all reports would be sent to the court, whose verdict on the cause of death would be final, he categorically stated.
Adding to the mystery, a handwritten 60-page note was found near Pul's body, titled 'My Thoughts', which was sealed by the police.
A case of unnatural death was registered and the state government had ordered a magisterial inquiry.
The state saw a major political churn last month with chief minister Pema Khandu along with 42 MLAs leaving the Congress and joining the Peoples' Party of Arunachal.
The 60-member state Assembly now has 11 MLAs belonging to the Bharatiya Janata Party, three to Congress and two Independents.
In a swift turn of events in state's unstable political canvas, senior BJP leader Tamyio Taga was sworn-in as minister on October 14, making the BJP coalition partner of Khandu-led PPA government to become an alliance of Northeast Democratic Alliance (NEDA) headed by Assam Minister Hemanta Biswa Sharma.
Election Commission on October 17 announced by-election to the Hayuliang Assembly constituency- which fell vacant after Pul's death- to be held on November 19.
The PPA and the BJP are planning to announce a joint candidate for the seat while Pul's third wife Dasanglu Pul is a frontrunner.
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