Mumbai,  A shroud of mystery continues to envelop the death of Thane businessman after his autopsy report remained inconclusive on the exact cause/s of his demise as the Opposition Bharatiya Janata Party aggressively demanded a probe by NIA, here on Saturday.

The autopsy report's findings and medical opinion are kept on 'reserve' though the viscera have been preserved and sent to the Sir J. J. Hospital here for further analysis, officials said.

Though there are reportedly no visible injury marks on Hiren's body, his family and friends have dismissed the 'suicide by drowning' as he was an expert swimmer, besides eyewitnesses who have questioned why his mouth was gagged with 5-6 handkerchiefs.

Hiren, 48, came into the limelight after his stolen SUV, a Scorpio was abandoned near Antilia, the home of industrialist and Reliance Industries Ltd Chairman Mukesh Ambani on Feb. 25.

The next day, the police found 20 gelatin sticks in it besides a purported threat letter to the Ambani family, triggering a sensation in corporate and political circles.

Exactly 10 days later, Hiren's body was fished out of the wetlands in Thane Creek near Mumbra town on Friday morning, stoking a massive political row.

The owner of a car accessories business, Classic Car Decor and a resident of Vikas Palms complex, Hiren's family accepted his mortal remains from the Chhatrapati Shivaji Maharaj Hospital in Kalwe and performed his last rites late on Saturday evening.

The state government late on Friday handed over the probe to the Anti Terrorist Squad (ATS) which has started its investigations.

Deputy Commissioner of Police (Zone I) Avinash Ambure said that the autopsy report was shared with the family, but declined further details as the probe is underway.

The President of Thane Vyapari Sangh Devi Jain demanded a thorough probe and the causes leading to Hiren's death, whom he described as a good family-centric man, financially sound with no vices.

Meanwhile, a letter claimed to be penned by Hiren on March 2 to Chief Minister Uddhav Thackeray, Home Minister Anil Deshmukh, Mumbai Police Commissioner Param Bir Singh, Thane Police Commissioner Vivek Phansalkar, spoke of police harassment after the recovery of his SUV with the gelatin sticks and threat letter.

Police are also trying to verify Hiren's wife Vimala's statement that on Thursday he was summoned by one officer Tawde from Kandivali Crime Branch who asked him to meet him near the Thane Creek.

As the matter snowballed into a political row, Minister Deshmukh held a review meeting with Director-General of Police Hemant Nagrale.

The BJP targeted the Maha Vikas Aghadi government alleging failure on all fronts and vociferously demanded that the case be handed over to the NIA, besides senior MP Narayan Rane wanting President's Rule in Maharashtra.

BJP State President Chandrakant Patil said that prima face, the death of Hiren is a 'murder' and sought a probe by NIA.

However, Shiv Sena MP Sanjay Raut said that the Mumbai ATS is capable of probing the case and urged that Hiren's death should not be politicised.

"It will be wrong to politicise the (Hiren's) death and put the government in the dock... Doubts are being raised whether his death was a suicide or a murder. The police are investigating. He was also an important witness in the (SUV) case," Raut said.

Lashing at the MVA, BJP MLA Nitesh Rane said in series of tweets: "Disha Salian - was happy but committed suicide, Sushant Singh Rajput - was ambitious but committed suicide. Pooja Chavan - was too strong but committed suicide, Mansukh Hiren - wife says he can't commit suicide! This is what happens in Maharashtra under the MVA!"

Several BJP leaders met Hiren's family members and a large number of people including businessfolk turned up for Hiren's funeral held late on Saturday.