A semi-burnt body of a senior citizen was found at his Sector 4 residence on Tuesday.
The body of the victim, Virender Kanwar (75), was found in a decomposed state, the police said.
Kanwar had been residing at the house with his mentally-challenged son Banni (40). The police have not ruled out any foul play in this case.
The incident came to light after Kanwar's milk vendor complained of stench coming from the house.
He immediately informed the neighbours who then summoned the police.
"When our team reached the house, it was locked from the inside. We broke open the door and found Kanwar's half burnt body. His mentally-challenged son was sitting naked next to him. The body was decomposed and it seems that he died three to four days ago. The body has been sent for a postmortem," said a police official.
The neighbours alleged that at several occasions, Banni came out naked and damaged their cars and houses.
Once he allegedly set fire to his own house. They also alleged that they had filed several complaints against him with the police.
"It is difficult to ascertain the cause of Kanwar's death. We are awaiting the postmortem report," said Surender Pal, DCP (west), Gurgaon.
"We are investigating the matter from all the angles. It is too early to reach at a conclusion," said a police official.
The police have handed Banni to their relatives. Kanwar's daughter will arrive in the city from Mumbai on Wednesday.
Kanwar's wife had died earlier while his other son was killed in a road accident some years ago, the police said.