Bodies of a mother and her son were found at their residence in Mumbai's Mira Road area on Tuesday.
A suicide note was recovered from the man's laptop leading to suspicion, that he first killed his mother and later took his own life, police said.
The deceased have been identified as Vaikateshwaran Gopal Iyer, 42 and Meenakshi Iyer, 75.
Police reached the spot after neighbours complained of foul smell in the building, and the bodies were later sent for post-mortem.
"We received information from the neighbours who complained about a foul smell emanating from Iyer's flat. We immediately reached the spot and found both mother and son dead in their flat," police official Shekhar Dombe said.
The mother's body was found lying in a pool of blood, while there were no injury marks on the man's body, neighbours who were present at the spot when police broke into the house said.
According to the residents of the building, both mother and son were not seen in the premises over the past four days.
The Iyer's had moved to Mumbai in 2017 and were residing at Marigold Apartments in Mira Road area. Their agreement with the landlord had lapsed in April, but the deceased man had sought two months time to vacate the flat, stating that he had some prior engagements.
A case has been registered in the matter and further investigation is underway.