Police initially registered a case under Section 174 Cr P C (unnatural death) when Reddy's body was found by his staff early in the morning.
After post-mortem in the local government hospital, police confirmed the case was altered to Section 302 IPC that relates to murder.
His party,YSR Congress, demanded a CBI investigation into the case even as the Andhra Pradesh government constituted a Special Investigation Team, headed by CID Additional Director General of Police Amit Garg, to probe the death.
Terming the killing as a 'politically mean act," he told reporters in Pulivendula after visiting the spot that only a CBI investigation would bring out the truth.
Justice would be done only if a third party probed the case, he said, adding they had no faith in the state police.
He also alleged that the state government was fabricating evidence to portray Vivekananda's death as natural.
"They (government) came out with a letter purportedly written by my uncle, naming a driver (as the culprit). How could a person write a letter while being killed,?" he asked.
This was the third unnatural death in the YS family that has a powerful political hold in Kadapa district.
Police said injuries were found on the forehead, head and its back, besides on the hand and thigh.
"We have gathered some clues in the case. We are questioning the former minister's household staff. Some fingerprints were also collected from the scene," Kadapa District Superintendent of Police Rahul Dev Sharma said.
"We have taken the case seriously and are investigating it from all angles," Sharma added.
The Chief Minister spoke with the DGP R P Thakur and other senior officials, asked them to conduct a thorough probe and not spare the guilty, said a CMO communique.
Naidu recalled Vivekananda's services as a public representative and extended sympathies to the bereaved family.
His death sparked a political row between TDP and YSRC.
"He actively took part in election campaign in Jammalamadugu yesterday. That he died suddenly gives rise to several suspicions. So we want a CBI investigation to bring out the facts," YSRC spokesperson Vasireddy Padma demanded.
State Animal Husbandry Minister C Adinarayana Reddy, who belongs to Jammalamadugu, took objection to YSRCs insinuation and said it has become a habit for the opposition to politicise everything.
"I also want to know the facts behind such a nice person's death. We too want an impartial inquiry, but YSRC leaders should stop mudslinging," he told reporters here.
Known to be a down-to-earth and genial person,Vivekananda was elected as MLA in 1989 and 1994 from his hometown Pulivendula in Kadapa district.
He was elected to the Lok Sabha from Kadapa constituency in 1999 and 2004 and to the Andhra Pradesh Legislative Council in 2009.
He had differences of opinion with his nephew Jagan Mohan Reddy after the latter quit Congress and established the YSR Congress and chose to stay back with the parent party.
He was reportedly alone at his residence in Pulivendula on Thursday night.
"There was no response when I went to his house this morning. I called his wife in Hyderabad over phone and she asked me not to disturb him.Later,the cook and other household staff reached the house but they too did not get any response.
I then went in through a side door and found Vivekananda's body in the bathroom, with blood clots in the bedroom and the bathroom. There were several injuries on his body," Vivekananda's personal assistant M V Krishna Reddy said.
He lodged a complaint with police, based on which the FIR was registered.
YSRC MP V Vijayasai Reddy expressed shock over the former minister's death.
"He was such a humble person who always engaged himself in public service. It is a huge loss to the YSRC and also the state," the MP said in a message.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)