Police initially registered a case under Section 174 Code of Criminal Procedure (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 Indian Penal Code that relates to murder.
The incident sparked a political slugfest between the opposition Yuvajana Shramika Rythu Congress and the ruling Telugu Desam Party with both trading allegations against each other.
Vivekananda Reddy's party, YSR Congress, demanded a Central Bureau of Investigation probe 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.
YSR Congress president Y S Jagan Mohan Reddy alleged that Chief Minister N Chandrababu Naidu was responsible for the death of his uncle.
Lashing out at the YSRC chief, Naidu told a press meet later that the slain leaders family appeared 'prima facie guilty' as they not only tried to hide the murder but also destroy vital forensic evidence.
Jagan Mohan Reddy and the YSRC blamed him, his son Lokesh and the TDP only for political gains, Naidu alleged.
"Truth is truth. Nothing can be hidden. They wanted to use a family members murder for political gains. Its a misfortune to have such a leader in politics," Naidu said, hitting out at the YSR Congress chief.
Rejecting Jagan Mohan Reddys demand for a CBI investigation, Naidu said the demand was raised only to get away from the case.
He asserted that only the state police would investigate the case.
Terming the killing as a 'politically mean act', the YSR Congress chief 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.
While the father Y S Raja Reddy was murdered in 1998, the eldest son M Y S Rajasekhara Reddy was killed in a helicopter crash in 2009.
Vivekananda Reddy was a two-time MLA, two-time MP and a one-term MLC. He served as agriculture minister in the N Kiran Kumar Reddy government in united Andhra Pradesh.
The 68-year old YSR Congress leader is survived by his wife and a daughter.
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 Telugu Desam Party 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 Amaravati.
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.
Vivekananda lost the by-election to his sister-in-law, Vijayamma in 2011. Subsequently, the family differences were sorted out and Vivekananda Reddy joined the YSRC.
Two days ago, he was seen at the Lotus Pond residence of Jagan Mohan Reddy in Hyderabad and on Thursday campaigned for the YSRC in Kadapa district.
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 first information report 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.
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