Rohit Shekhar Tiwari, son of late Uttarakhand chief minister ND Tiwari, died of "asphyxia" as he was strangulated and smothered, according to autopsy report.
Following the postmortem at AIIMS in Delh, police on Thursday registered a case of murder and transferred it to the Crime Branch for investigation, a senior officer said.
The autopsy was conducted by a medical board comprising five senior doctors of the All India Institute of Medical Sciences (AIIMS).
"The medical board unanimously concluded that the cause of death in this case is asphyxia as a result of strangulation and smothering. It is a sudden unnatural death, placed in the category of homicide," the head of the AIIMS' forensic department, Dr Sudhir Gupta, said.
The case has been transferred to the Crime Branch and it has started investigating the matter, the officer said.
Crime Branch officers visited Rohit Tiwari's residence on Friday and questioned his family members and domestic helps, police said, adding that a team of forensic experts also visited the house.
The officers are going through footage from CCTV cameras installed in and around the house to find leads, ascertain the sequence of events and track people who entered the house, they said.
Rohit Tiwari (40) died on Tuesday.He was brought dead to the Max Hospital in Saket in south Delhi.
Deputy Commissioner of Police (South) Vijay Kumar on Tuesday had said that Rohit Tiwari, a resident of Defence Colony in south Delhi, was brought to the hospital around 5pm in an ambulance and doctors declared him dead.
His mother Ujjwala Tiwari, who was admitted at Max hospital, received a call from her house about her son being "unwell and bleeding from the nose", he said.
"Max hospital received an emergency call from the residence of Rohit Shekhar Tiwari at 4:41 pm this (Teusday) afternoon. An ambulance brought Tiwari to Max Hospital, Saket, where he was declared brought dead at the emergency department," the hospital had said in a statement.
Narayan Dutt Tiwari died at the age of 93 on October 18, his birthday, last year.He, too, was undergoing treatment for age-related complications at the Saket hospital.
The Congress veteran, who had served in various positions at the Centre, was the chief of minister of Uttarakhand and Uttar Pradesh.
Rohit Tiwari joined the BJP ahead of the 2017 Uttarakhand assembly polls and had recently indicated he could join the Congress.